ARM 开发日记

       你突然离开我已经有一个月的，在这个一个月间，经历了很多事情，但很遗憾的事，自从你走后我再也没有完完全全的进入过晚间的状态，甚至连写点长篇东西的动力都没有，不能长时间的完全进入夜晚的状态，每天晚上依旧和之前一样，开着手机，等着你给我消息，可是我不知道你还会不会来，但是我还是那句话，不管你怎么样想的，完成我的诺言，好好做一个为期五年的奋斗计划，随时等着你回来。（现在是听着赵传的歌在写东西，好点）

      当你说要走的时候，我做了一件，令我不留遗憾的事情，23号对我说的，我24号一早就去买了一张当晚的T32票子，有个可能很“幼稚”的想法，希望在火车上碰到你，希望能在北京站看到你，希望能在六里桥见到你，希望能在宣化的北方大酒店遇见你，希望能再见到你！！！，可是一切都很不巧，一切也都很巧，火车上遇见两位邻座的，一个是学生一个是打工仔，我在他们身上前者看到了激情与朝阳，后者看到了勤劳和勇敢，他们给了我一种新的生活态度（或者说是渡过那最难熬的几天的理由）——理想是要有的，但是更需的激情，勤劳，勇敢。这样才能够去实现理想，于是我做了个180度掉头的决定：在你生活过的故乡走走，体验体验你的童年，从北京下了火车是25日下午的，我很感谢那个上文提到的学生，（他在北京念得书，地比较熟悉）给我指清了道路，当然我只知道六里桥长途车站，于是乎帮我买了地铁票，告诉我换乘公交的线路，送我上了地铁，我的行程由此开始的……

       到了六里桥，我在犹豫的要不要去宣化呢，应该当时的主要目的还是想去看看你，以及你的父母，可是没有具体地址，这点是我十分的犯难，我试图通过朋友以特定的方式来查询你的住址，很可惜，你登记的还是你上大学时候的集体糊口，我不知道该说这个很凑巧，我想了很久很久直到车要开了之前五分钟，我决定——去，不全因为你，还因为我要去感受你过去的一切。

     快四点的车上了京张高速，走出了城市，走出了繁华，走出了喧闹，走出了还算漂亮的北京，走进了古城，走进了市井，走进了宁静，走进了夜晚相当宁静的宣化古城，在北方大酒店下了车，感觉很宁静，宁静过头了，路上人少就不说的，店铺都关着，霓虹灯也是很阑珊，也许是刚下过雨的影响了，来宣化的路上，下了好大的雨，和司机聊了几句，他都没见过这么大雨，奇了在沙城的时候还暴雨呢，到了宣化，一滴雨都没了，我不知道这场雨是不是为我而下的，或者说是不是为我而停的，如果说都是的话，下着雨非常符合当时的心情，雨停也许是之后心情的写照吧！

       从北方大酒店那里开始，一个人走了很久很久，感觉到很累，心很累很累，毕竟来了宣化，近在咫尺，却不能见到你，你说我多不好受，走到不想走了，打了个车，夜晚溜了圈宣化，最后在宣化火车站前面找了个旅馆住了下来，那晚上不知道是坐火车累了还是因为我已经想好明天怎么过，暂时没什么新的心结，睡得初期的好，而且第二天早晨起来也没有习惯性的打喷嚏，我想也许是我特别适合这座古城吧，呵呵，

   早起后出门转了圈，古城宁静却也不失那分热闹，一条大街上都是卖早点的，有卖豆腐的，有卖卷饼多的，找个摊点，要了碗玉米糊糊，第一次吃这么稀的，感觉很香很香，有个特别的配菜很有意思，用包心菜的嫩叶炒炒当玉米糊的配菜，有点像我们这里的榨菜，很好吃。吃完了起身，环顾一下四周，默然的感到意思熟悉，不知道是昨晚横着走了一段路呢，还是因为让出租车司机转了圈，感觉一点都不陌生，很快，我就走到人民公园那里，这个你小时候，每周一去的地方，这点我非常的羡慕，到今天为止，我也很是羡慕，我的童年极大部分时间是在家里渡过的，因为父亲身体的原因不可能带我外出，而我的母亲她要上常日班，到了周末也想好好休息一下，我就把我的一些想玩的想法给收了起来，陪我渡过童年的最多还是那几样东西（当然这段指的是还没学会跟小朋友外出的时间）：积木，七巧板，和棋类，我的小时候的个性就是 一个人呆着挺好的，不喜欢和人扎堆。就是这样被练出来的

扯远了，回正题，此时初升的太阳烤在你的背后，挺舒服的，有一种说不出的味道，看着射向人民公园大门字牌的阳光把字牌照的红艳艳的，感觉真的很好很好，非常的美，一种古城的宁静美出现的，此刻我并没有进去，而是继续走了下去，走向了“拱极楼”，好漂亮的城楼啊，我在南方从来没见过，不说气势如何，感觉大小就比杭州的鼓楼大多的，（虽然都是钟鼓楼）

这个是我拿手机拍的，手机上效果看不怎么好，拉到电脑上看，特别的美，天蓝墙灰真的很亮，是我想象所期望的养老的地方，真的，有一种说不出的亲切感，

刚拿到板时，运行板载的Qtopia 系统做测试的时候发掘到一个问题，板子不会自动dhcp获得ip地址，但是通过查看bin文件，发掘bin中存有dhcp的程序，只是没有伴随系统的启动。百思不得其解，为什么不用dhcp为用户提供方便呢，而要求用户通过console口，执行udhcpc &来启动dhcp服务，这样不是很麻烦，？想了n天，结果只有一个，固定ip平台。观察其bin文件，发现其启动了vsftp，也就是在板子启动的那一刻，这机器就成了一台ftp服务器，岂能不固定ip，当然这样同时给用户带来不便，有没有办法两全其美吗？

相信有，顺序执行，先dhcp自动分配，发送discover包，无应答，执行原固定ip/得ip话，继续，登陆之后提示当前ip：可惜最近没有时间改写bin的，回头再改吧！

       上周买了想很久的arm开发版，虽然很花钱，但是很开心，开心的同时却听到了汶川大地震的消息。在此首先向本次地震的遇难者表示一下哀思 ，并且对冲在一线的救援人员和那些有着社会责任心的企业家。有着爱心的全体华人表示最崇高的敬意！  愿生者坚强，死者安息！大爱中华行！

    转回话题，这次买的s3c2440+4.3TFT触摸屏，板栽linux的改版移植系统Qtopia，通过console口使用超级终端调试，进入系统自检平台一切正常，结果就是进不了linux的控制台，结果搞了半天是com口设置出了问题，数据流控制 误选了硬件控制吸取教训，通过dhcp分配，得到ip等信息，成功调试上网

 

A History of U.S. Military Satellite Communication Systems

Donald H. Martin

Twenty-five hundred years ago the Chinese general Sun Tzu wrote, "If you know the enemy and know yourself, you need not fear the result of a hundred battles." But how are U.S. soldiers, operating covertly in unfamiliar and hostile territory, to know where their allies are, where their enemies are, and what each is doing? How are they to receive commands and report status? The answer is satellite communications.

Satellite communication has been a vital part of the United States military throughout the space age, beginning in 1946, when the Army achieved radar contact with the moon. In 1954, the Navy began communications experiments using the moon as a reflector, and by 1959, it had established an operational communication link between Hawaii and Washington, D.C.

As the U.S. space program grew in the 1960s, the Department of Defense (DOD) began developing satellite communication systems that would address the special requirements of military operations. In addition to protection against jamming, these needs included the flexibility to rapidly extend service to new regions of the globe and to reallocate system capacity as needed.

The goal of these systems has been to provide communications between, and to supply information to, military units in situations where terrestrial means of communication are impossible, unreliable, or unavailable. This goal was partly realized with the earliest DOD communication satellites, and as satellite and communications technology has improved, the goal has been realized to a much greater extent.

Early DOD satellite communication experiments led to initial operational systems, which evolved to a complete military satellite communications (milsatcom) architecture encompassing DOD's unique requirements. Within this milsatcom architecture, different systems were developed for three broad populations of users: wideband, tactical, and protected. Each is characterized by its own satellite designs, Earth terminals, and applications.

The Aerospace Corporation has been a key player throughout this history. From the early days of the space age, the company has taken a significant role in the development and deployment of military communication satellites. Aerospace participates in all planning efforts for these satellite systems, including studies of requirements, surveys of current and projected technologies, and analyses of multiple alternatives to satisfy requirements (see Milsatcom Timeline).

Aerospace assists DOD in the definition of technical requirements for satellite systems. As satellite hardware is designed, built, and tested, Aerospace reviews the designs, analyses, and test plans; observes testing; and studies test results. It also assists with launch preparations and support of on-orbit operations.

The First Satellite Communication Programs

The first U.S. military communication satellites were of an experimental nature and used low-altitude orbits. They were developed to provide basic experience with satellites and to explore what satellite communications could do. Later systems would see actual military field use.

SCORE

The first artificial communication satellite, Project SCORE (Signal Communication by Orbiting Relay Equipment), was launched in 1958, primarily to show that an Atlas missile could be put into orbit. The secondary objective was to demonstrate a communications repeater built into the missile. A repeater receives a signal, amplifies it, and then retransmits it.

The Army Signal Research and Development Laboratory created the repeater by modifying commercial equipment. Two redundant sets of equipment were mounted in the nose of the SCORE missile. Four antennas were mounted flush with the missile surface, two for transmission and two for reception.

SCORE's other equipment included two tape recorders, each with a four-minute capacity. Any of four ground stations in the southern United States could command the satellite into playback mode to transmit the stored message or into record mode to receive and store a new message. One was a Christmas message from President Dwight D. Eisenhower.

Courier

The objective of the Courier program was to develop a satellite of higher capacity and longer life than SCORE for use in communication tests and assessments of traffic-handling techniques. Courier's primary operating mode, like SCORE's, was store-and-dump (storing data onboard to be later "dumped," transmitted to a ground receiving station when one is in sight of the satellite) using tape recorders. Unlike SCORE, however, Courier was a self-contained satellite.

The first Courier launch was unsuccessful because of a booster failure; the second, in October 1960, succeeded. Communication tests were performed by ground terminals in New Jersey and Puerto Rico. The satellite performed satisfactorily until 17 days after the launch, when a command-subsystem failure stopped communications.

Advent

Courier was a relatively simple satellite. Since it was designed for experimental use, the Advanced Research Projects Agency undertook the Advent program in 1960, concurrent with the Courier program, to provide an operational military communication satellite. The concept for Advent was far more sophisticated than the technology available at the time; hence a number of problems occurred in development, and it was canceled in 1962.

A few of West Ford's 480 million copper wires. (IEEE)

West Ford

West Ford grew out of a Lincoln Laboratory study on secure, survivable, reliable communications. The West Ford "satellite" consisted of 480 million thin copper wires, each about 1.5 centimeters long. The 19.5 kilograms of wires were dispensed from an orbiting container in 1963. During the first few weeks after launch, voice and data were transmitted from Pleasanton, California, reflected by the wires, and received at Westford, Massachusetts, the source of the project name. Four months later, when the wires were further dispersed, they could reflect only very low-rate data from Pleasanton to Westford. Because of this low capacity and the growing use of active satellites, no more experiments like West Ford were attempted.

Early Operational Satellite Communication Programs

Policy debates in the early 1960s addressed the question of whether military and civilian communication satellite systems should be separate or combined. Aerospace participated in 1964 congressional hearings that resulted in a government policy to establish and maintain separate military satellite communication systems to satisfy unique and vital national-security needs that commercial systems could not satisfy. The government was still able to use commercial satellites if those satellites provided links of the required type and quality in a timely manner at reasonable cost.

Lincoln Experimental Satellites

After the West Ford program, Lincoln Laboratory continued its investigation of space technology for application to military communications, developing the Lincoln Experimental Satellites (LES) series.

Aerospace and Air Force program managers with a model of an IDCSP satellite in 1966. The polyhedral body is covered with solar cells, and the antennas extend to the right of the body. (The Aerospace Corporation Archives)

LES-1 through LES-4 carried equipment for communication and propagation experiments. The primary experiment on LES-1, -2, and -4 was a repeater and an eight-horn electronically switched antenna. Frequencies were in the 7900-to-8400-megahertz range for the uplinks (the Earth-to-satellite transmissions) and the 7250-to-7750-megahertz range for downlinks (satellite-to-Earth transmissions)—a combination used by later military communication satellites that is called X-band (see sidebar, Frequency Selection).

The LES-3 frequency was in the portion of the spectrum that DOD called ultrahigh frequency (UHF), commonly used for DOD tactical communications among small terminals. LES-3 was intended to investigate the extension of UHF communications to links with satellites. It transmitted a signal to be used in atmosphere-propagation measurements.

The first four LES satellites were launched in 1965. Although not all reached their intended orbits, they were used for more than a year. They demonstrated payload operations in space, supported propagation measurements, and helped improve ground equipment for both communications and satellite control (see sidebar, A Communications Satellite Payload).

The LES-5 and -6 satellites had communications equipment that operated in the UHF band. Both had transmitter designs with significant improvements over those of prior satellites.

LES-5 was launched in 1967. Airborne, shipborne, and fixed and mobile ground terminals were involved in a large number of successful tests with LES-5, which operated until 1971. LES-6, used in similar tests, was launched in 1968. These satellites clearly demonstrated that reliable communications could be extended to military units equipped with small terminals.

Eight IDCSP satellites mounted on a launch dispenser in preparation to be launched from Cape Canaveral, Florida, on a Titan IIIC launch vehicle. (U. S. Air Force)

Initial Defense Communication Satellite Program

When the Advent program was canceled in 1962, a recommendation was made for another program that would be operational, not experimental. As a result, the Initial Defense Communication Satellite Program (IDCSP) was created. Its design principle was simplicity. Each IDCSP payload had a single repeater with a capacity of about 10 voice circuits or 1 megabit per second of data when communicating with large terminals on Earth.

Seven IDCSP satellites were launched in 1966 with additional groups of three to eight satellites launched in 1967 and 1968. Twenty-eight satellites were placed into orbit, operating for periods ranging from one to ten years. The IDCSP satellites drifted in orbits slightly below geostationary altitude. In contrast, almost all subsequent DOD communication satellites operated in the geostationary orbit (see sidebar, The Geostationary Orbit).

In 1967, increasing military activity in Vietnam led to the establishment of an operational communication link that used IDCSP. In this link, digital data were transmitted from Vietnam to Hawaii through one satellite and on to Washington, D.C., through another. In 1968, the system was declared operational, and its name was changed to Initial Defense Satellite Communication System.

Tactical Communication Satellite

The IDCSP satellites and the advanced satellites that followed them were for strategic communications between large-antenna, fixed or transportable ground stations and large shipborne equipment. The Tactical Communication Satellite (Tacsat), following the Lincoln satellites, was designed for a complementary function: operation with small land-mobile, airborne, or shipborne tactical terminals.

The Tacsat communication payload was designed with both UHF and X-band capabilities to permit operation with a wide variety of terminals. The requirement to operate with small terminals called for the use of high-power transmitters, which necessitated a very large, cylindrical body to provide the required solar-cell area. The need for the large body in turn required the development of a new stabilization technique, which was refined and subsequently applied to many commercial communication satellites.

The Tacsat satellite; the large cylinder was covered with solar cells, and the five helixes were the UHF antenna.

Tacsat was launched in 1969. On-orbit testing was done with a variety of terminals, including large ground stations, mobile ground stations, aircraft, and ships. Tacsat was used for operational support of Apollo recovery operations; it connected the aircraft, the aircraft carrier, and the ground stations. Military use, especially of the UHF band, was extensive. Operations continued until an attitude-control failure in 1972.

Milsatcom Architecture

By the early 1970s, DOD had determined the need for a milsatcom architecture to guide the development of technology and programs that would be responsive to military users' requirements and realizable within the DOD budget. In 1973 the Defense Communications Agency (DCA), now the Defense Information Systems Agency, was assigned responsibility for developing this architecture.

The first comprehensive milsatcom architecture, published in 1976, has been refined several times since then. It has three segments: wideband, mobile and tactical (or narrowband), and protected (or nuclear-capable). Within each segment is a mix of users similar enough to be supported by a common satellite system.

Aerospace participated from the beginning in the development and refinements of this architecture. The DCA office that directed the architecture work was headed from inception until 1976 by an engineer on leave from Aerospace. Additionally, Aerospace simulators have been used and refined over many years for studying the performance of architectural options in various military scenarios.

Wideband Systems

Users of the wideband segment primarily have fixed and transportable land-based terminals; a few have terminals on large ships or aircraft. Their data rates vary from moderate to high, and their connectivity may be point-to-point or networked at distances ranging from in-theater to intercontinental. The wideband systems are the Defense Satellite Communication Systems (DSCS) II and III and the Global Broadcast Service (GBS) payload on the UHF Follow-On (UFO) satellite.

Defense Satellite Communication System II

The IDCSP satellites were the DSCS Phase I space segment. They demonstrated that satellite communications could satisfy certain DOD needs, so in 1968, DOD decided to proceed with the development of satellites for DSCS Phase II.

A DSCS heavy terminal with an 18.3-meter-diameter antenna, used at major communication nodes. (U. S. Department of Defense)

DSCS II satellites had a command subsystem, attitude control and stationkeeping capabilities (the ability, on command from Earth, to adjust satellite orientation or or-bital position), and multiple communication channels with multiple-access capability. IDCSP had none of these features; however, the DSCS II design was compatible with modified Phase I ground terminals as well as new terminals specifically built for Phase II.

The DSCS II communication payload had four channels with various combinations of bandwidth and antennas. The combinations provided the flexibility to handle a wide variety of links and to communicate with many sizes of terminals. Initial terminals constructed at major nodes had 18.3-meter-diameter antennas.

The DSCS II program began with six satellites launched in pairs, the first in 1971. Major technical problems caused the satellites to fail in 1972 and 1973. Analyses of these problems, with significant Aerospace contributions, provided the basis for design modifications for the next satellites. By 1989 a total of 16 satellites were launched to establish and maintain an orbital constellation with at least four active and two spare satellites. All are now out of service and have been moved above the geosynchronous orbit to prevent interference with active satellites.

DSCS III

The DSCS program was planned for long-distance communications between major military locations. During the system's evolution, both the number and variety of terminals increased as more DOD units sought to benefit from satellite communications. By the 1990s, a majority of DSCS terminals fell into the categories of small, transportable, or shipboard. Phase III DSCS satellites were developed to operate in this diverse environment.

The January 2000 launch of a DSCS III satellite on an Atlas IIA launch vehicle from Florida. (International Launch Services. Photo by Carlton Bailie)

The primary DSCS III communication payload operates in the X-band and has eight antennas that can be connected in various ways to the six transponders ("transmitter/responders"). Each transponder can be configured to serve a specific type of user requirement. Besides Earth-coverage antennas, the satellite has one multibeam receiving antenna, which can form a beam of variable size, shape, and location, and two similar multibeam transmitting antennas.

DSCS III development started in 1977. The first satellite was launched in 1982, and 11 additional satellites have been launched since then. All are operational. Five occupy the prime operating locations of the DSCS constellation, which are spaced around Earth in geostationary orbit. The others, spares for the five primary satellites, augment the capacity and coverage of the constellation.

To satisfy increasing user needs, the last four DSCS III satellites were enhanced to improve their communications capacity by 200 percent, with up to a 700-percent increase in capacity to tactical users (those with small terminals) in certain scenarios. Aerospace played a key role in identifying and analyzing options for this enhancement program—an important activity, since the number of tactical users increased greatly over the past two decades. Many use truck- or trailer-mounted terminals with 2.4-meter-diameter antennas. Such terminals do not operate while in motion, but can be set up at an unprepared site by two or three people in less than 30 minutes.

Global Broadcast Service

The Global Broadcast Service (GBS) is another part of the milsatcom architecture's wideband segment. Its mission is to deliver high-rate intelligence, imagery, and map and video data to tactical forces using small, portable terminals. Phase I of GBS used a commercial satellite and a limited number of commercial receive terminals. Phase II uses the GBS payload on UFO satellites 8 through 10. This payload uses 30-gigahertz uplink and 20-gigahertz downlink frequencies, often called Ka-band. Phase III will be developed in the future.

The UFO satellite in orbit; the large structure on the front of the satellite body is the UHF transmit antenna, the small square toward the bottom of the body is the UHF receive antenna, and the equipment on the top is the GBS antenna apparatus.

Information to be disseminated through GBS is assembled into a broadcast stream transmitted to the satellite and rebroadcast to a large number of users in one of several spot-beam coverage areas. (Spot-beam antennas focus on a limited area of Earth.) Each user, typically a small military unit, has an easily moveable set of receiving and display equipment.

Mobile and Tactical Systems

Users in the mobile-and-tactical segment of the architecture are characterized by small terminals with relatively low-gain antennas; they are located on ships, aircraft, and land vehicles. Data rates are low to moderate, and connectivity is typically in networks at distances ranging from in-theater to transoceanic. Systems in this segment are the Fleet Satellite Communications System, the Leasat program, and the UHF Follow-On (UFO) program.

Fleet Satellite Communications

Tacsat and LES-5 and -6 were experimental satellites that demonstrated UHF (225- to 400-megahertz) links with mobile terminals. These satellites were used for numerous tests, and Tacsat and LES-6 provided a limited operational capacity for DOD. The Fleet Satellite Communications (FLTSATCOM) system was DOD's first operational system (dedicated to supporting military operations) for tactical users.

A ground mobile forces satellite terminal with the 2.4-meter antenna; communications electronics are inside the truck. (U. S. Department of Defense)

FLTSATCOM served Navy surface ships, submarines, aircraft, and shore stations. The largest antenna, used for UHF transmissions, was a 5-meter-diameter paraboloid that had a solid center section and a deployable outer mesh section. The separate UHF receiving antenna was a single helix deployed to the side of the large paraboloid. Most links were in the UHF band.

The first FLTSATCOM was launched in 1978, the last in 1989. For this program, as for others, Aerospace performed a structural dynamics analysis of the satellites as subjected to launch vehicle loads.

One FLTSATCOM satellite was damaged during ascent and could not be used. The others operated as expected and greatly exceeded their five-year design lives. They have been removed from service and replaced by UFO satellites.

Leasat

In 1976 and 1977 Congress directed DOD to increase its use of leased commercial satellite services, and specifically applied this direction to the tactical satellite system that would follow FLTSATCOM. The result, the Leasat program, primarily served the Navy, plus Air Force and ground forces mobile users. FLTSATCOM terminals were used with Leasat. Leasat had four types of communication channels, with characteristics very similar to the FLTSATCOM channels, and four communications antennas: two X-band and two UHF; all were Earth-coverage.

The contract for Leasat development was awarded in 1978 and called for five years of communication service to be provided at each of four orbital locations. The first two launches took place in 1984, the last in 1990. Leases on satellites 2, 3, and 5 were extended into 1996. The Leasats have been removed from service and replaced by UFO satellites, with the exception of one now in use by the Australian Defence Forces.

UFO

The UFO satellites replaced the Navy's FLTSATCOM and Leasat satellites. The Navy's requirements for UHF capacity had grown considerably since the first FLTSATCOM launch in 1978. At that time, four operational satellites plus one orbiting spare were planned. The 1991 constellation was double that size and included six FLTSATCOMs and four Leasats. These satellites were still functioning properly at the end of 1995, but by 1999, all had been removed from service.

The Army's Enhanced Manpack UHF Terminal, which is capable of being carried, set up, and used by a single soldier, communicates via the UFO satellites. (U. S. Army)

The Navy replaced the older satellites with a constellation of eight UFOs, plus one spare. The UFO satellites have more channels than the earlier satellites and are designed to be compatible with the more than 2000 UHF terminals used with FLTSATCOM and Leasat. Satellite capability increases have led to a reduction of terminal sizes. Some terminals can be carried, set up, and used by one person, thus minimizing the burden on military users and increasing the number of military units that can benefit from satellite communications.

The UFO contract was awarded in 1988; a total of ten were ordered by 1994. A contract for an eleventh satellite was signed in 1999. The first UFO was lost as a result of a launch vehicle problem, but the next nine, successfully launched between 1993 and 1999, are in use. Satellite 11 will be launched in 2003. Besides performing its usual systems engineering tasks throughout the UFO program, Aerospace also developed a telemetry analysis workstation and installed it in a satellite control center.

Protected Systems

Mobility characterizes users of the protected segment of the milsatcom architecture, whether they are on ships, aircraft, or land vehicles. They accept very low to moderate data rates in exchange for considerable protection of their links against physical, nuclear, and electronic threats. Systems in the protected segment of the milsatcom architecture are the Milstar system and the Air Force Satellite Communications (AFSATCOM) and extremely high frequency (EHF) payloads.

AFSATCOM

AFSATCOM served Air Force strategic aircraft, airborne command posts, and ground terminals. AFSATCOM satellite payloads are on the FLTSATCOM satellites and on several satellites situated in high-inclination orbits to provide coverage of the north polar region, which is not visible from equatorial satellites. AFSATCOM also uses a single-channel transponder on DSCS III satellites.

AFSATCOM uses a mix of UHF and X-band frequencies with antijamming protection for most of its uplinks by frequency-hopping (rapid switching of frequencies during transmission). A portion of the Milstar communications payload continues the AFSATCOM mission.

FLTSATCOM EHF

FLTSATCOM satellites 7 and 8 contained an EHF payload (44-gigahertz uplink and 20-gigahertz downlink) called the FEP (FLTSATCOM EHF Package). FEP was developed to demonstrate operational capabilities of EHF terminals and prove key functions of the Milstar system. This payload had both Earth-coverage and spot-beam antennas, and it processed received signals before their downlink transmission. Both links were frequency-hopped.

Milstar Block I and II

The Milstar system is designed to emphasize robustness and flexibility. The term "robustness" here refers to the ability to operate under adverse conditions, including jamming and nuclear attack. Aerospace played a key role in assessing Milstar system performance against a DOD-validated threat model. "Flexibility," in this context, is the ability to provide worldwide unscheduled access and worldwide connectivity to terminals on all types of platforms.

The Milstar program includes two Block I and four Block II satellites. These blocks are also known as LDR (low data rate) or Milstar I, and MDR (medium data rate) or Milstar II. The block change resulted from a 1990 program restructure in response to global political changes.

The Milstar satellite in orbit with the two equipment wings and two longer solar-array wings deployed; various antennas are visible on the equipment wings. (Lockheed Martin Missiles and Space)

Relaxation of survivability requirements and improvements in satellite electronics allows the MDR satellites to provide robustness and flexibility for 32 MDR channels, for single-user data rates up to 1.5 megabits per second, in addition to the 192 LDR channels, for single-user data rates up to 2.4 kilobits per second. Aerospace was a leader in the development of the standard for the LDR and MDR waveforms.

The Milstar system has three segments: mission control, terminal, and space. The mission control segment plans mission activities, allocates system resources, tests and controls the satellites, and resolves satellite anomalies. It includes a fixed site as well as mobile units. Intersatellite crosslinks enable monitoring and control of all Milstar satellites from a single location.

The terminal segment, developed by the Air Force, Navy, and Army, contains more than 1000 terminals of many types; some are vehicle-transportable or human-portable, while others are located at fixed sites or on airborne command posts or other aircraft, ships, or submarines. Antenna diameters vary from 14 centimeters for submarine terminals to 3 meters for fixed command-post terminals.

The space segment consists of the Milstar satellites. Each has a central bus, two payload wings, and two solar arrays. At the outer end of each wing is a crosslink antenna. Other antennas are mounted on the wings. Features that support the system's robustness include frequency-hopping, extensive onboard processing, and crosslinks. Features that support flexibility include multiple uplink and downlink channels operating at various rates; multiple uplink and downlink beams, including agile beams; and routing of individual signals among uplinks, downlinks, and crosslinks.

The Block I satellites were launched in 1994 and 1995. Aerospace had a lead role in the analysis of one launch-vehicle failure and another anomaly just prior to the first launch, and provided launch-readiness verification for the Milstar 1 launch vehicle. The first Block II satellite was lost because of a launch problem. The second was launched in 2001; it and the Block I satellites are in operation. The third was launched in January, 2002. The last one is scheduled for launch in November, 2002.

UFO and Interim Polar EHF

Beginning with the fourth satellite in the UFO series, an EHF communications payload compatible with Milstar terminals was added to that satellite. An enhancement to the EHF payload beginning with UFO 7 doubled its communication capacity.

The EHF payload accommodates multiple uplinks distributed between the Earth-coverage antenna and the deployed steerable spot-beam antenna. Each uplink is time-shared by multiple users. The downlink (at 20 gigahertz) is a combination of all the uplinks (at 44 gigahertz). Both links are frequency-hopped.

The Interim Polar Program adapted the UFO/EHF payload for use on host satellites in high-inclination orbits. These payloads communicate with military forces operating above 65 degrees north latitude, where visibility to geostationary-orbit satellites is poor or impossible. The first launch with an interim polar payload was in 1997. Two launches remain, in 2003 and 2005.

Summary

U.S. military satellite communications have improved and expanded greatly over the past four decades, from SCORE through DSCS III, UFO, and Milstar. Capabilities have grown dramatically with the development of satellite and electronics technologies. Higher-power and wider-bandwidth satellites have enabled increased information transmission to an ever-wider assortment of terminal types deployed with an increasing number and variety of military units.

Throughout this history, and now, Aerospace has been involved in every phase of development and deployment of DOD satellite communication systems, from concept development and requirements definition through design and test reviews to launch preparations and on-orbit testing and operations. Aerospace regularly applies lessons learned in the course of one program to all DOD satellite programs.

As military satellite communication systems improve, they continue to provide information superiority to the U.S. military. This enables our military forces to remain dominant in the increasing speed and diversity of their actions during times of peace as well as times of conflict.

Further Reading

1. Air Force Link, fact sheets (Space fact sheet list includes DSCS, Milstar, UFO), http://www.af.mil/news/indexpages/fs_index.shtml, accessed January 2, 2002.
2. F. E. Bond and W. H. Curry, Jr., "The Evolution of Military Satellite Communications Systems," Signal, Vol. 30, No. 6 (March 1976).
3. W. H. Curry, Jr., "The Military Satellite Communications Systems Architecture," Paper 76-268, AIAA/CASI 6th Communications Satellite Systems Conference (April 1976). Reprinted in Satellite Communications: Future Systems, Progress in Astronautics and Aeronautics, Vol. 54, D. Jarett, ed. (1977).
4. I. S. Haas and A. T. Finney, "The DSCS III Satellite—A Defense Communication System for the 80's," AIAA 7th Communications Satellite Systems Conference (April 1978).
5. P. C. Jain, "Architectural Trends in Military Satellite Communications Systems," Proceedings of the IEEE, Vol. 78, No. 7 (July 1990).
6. D. H. Martin, Communication Satellites, Fourth Edition. (The Aerospace Press, El Segundo, CA, and AIAA, Reston, VA, 2000).
7. P. S. Melancon and R. D. Smith, "Fleet Satellite Communications (FLTSATCOM) Program," Paper 80-0562, AIAA 8th Communications Satellite Systems Conference (April 1980).
8. D. N. Spires and R. W. Sturdevant, "From Advent to Milstar: The U.S. Air Force and the Challenges of Military Satellite Communications," Ch. 7 in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed. (NASA History Office, Washington, DC, 1997); also Journal of the British Interplanetary Society, Vol. 50, No. 6 (June 1997).
9. V. W. Wall, "Satellites for Military Communications," Paper 74-272, AIAA 10th Annual Meeting (January 1974).
10. W. W. Ward and F. Floyd, "Thirty Years of Research and Development in Space Communications at Lincoln Laboratory," The Lincoln Laboratory Journal, Vol. 2, No. 1 (Spring 1989).

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