Micro-Eyes in Space
DEVELOPMENT IS UNDER WAY FOR MINIATURE SATELLITES THAT WILL ENABLE A MORE RESPONSIVE, EFFICIENT FLEET.
In an ideal scenario, the warfighter has access to a mix of sensor systems on the ground, in the air, in space and in the sea. In the space arena, this scenario is moving closer to reality, thanks to the development of microsatellites that will be able to talk with each other and with big satellites.
Prominent among those microsatellites is the TacSat program, being carried out by the Air Force Research Laboratory (AFRL) and the Office of Naval Research (ONR). The TacSat program is part of the Responsive Space initiative, which aims for flexible and affordable space systems. It involves three key areas: satellites, launch and operations. Currently, designing and developing a surveillance satellite could take more than 10 years, and then roughly a year to prepare and launch the spacecraft, and then perhaps weeks to activate payloads once they reach orbit. Responsive Space also involves better interoperability, such as plug-and-play interfaces and modular structures, as well payloads that support multiple missions.
“We believe we will give the soldier on the ground the ability to control a spacecraft payload. That’s going to be a ground-breaking sort of development for the way we use spacecraft,” said Peter Wegner, the Responsive Space Lead for AFRL, at Kirtland Air Force Base, N.M.
If the experiment goes as planned, a tactical user will be able to upload commands directly to the spacecraft, have it carry out the imaging and then downlink that imagery within minutes.
Warfighters would be able to control or communicate with the satellites with existing communications and imagery dissemination systems, like a Common Data Link radio. There may also be the ability to communicate with the satellite directly with hand-held UHF radios.
FAMILY OF TACSATS
Definitions of microsatellites vary, but as a general rule, they range in weight from about 10 kilograms to 100 kilograms. (A nanosat is up to roughly 10 kg, or up to 100 kg, depending on one’s definition.) The TacSat weighs about 800 pounds.
The total mission for a TacSat is estimated to cost about $50 million (as compared with hundreds of millions or billions of dollars for conventional satellites), which includes the spacecraft, the launch, a year of operations and payloads. Rather than piggybacking on launches of other satellites, the TacSat will have stand-alone launches dedicated to a TacSat.
The TacSat program is a test bed for essentially three different areas. “We’re exploring technologies that will enable the development of small, low-cost satellites fairly rapidly,” remarked Wegner. “We’re also exploring CONOPS (concept of operations) for those experiments. And we’re exploring different acquisition methods such as leveraging things being done in the airborne world, like unmanned aerial vehicle (UAV) sensors and payloads, and porting those over to spacecraft.”
The TacSat program is aimed to facilitate getting satellites into orbit quickly. Whereas it may take several years to develop and launch a conventional satellite, the goal is to launch the TacSat within 18 months from the beginning of the program. “I think we’ll be probably the closest to that on Tac- Sat-3 for the first time,” he observed. Once the TacSat-3 program is well established, AFRL plans to try to get a satellite into orbit within six days. “But that probably won’t be until at least 2010,” he said.
There are currently four TacSat programs underway: TacSat-1 through TacSat-4.
• TacSat-1 is led by the Naval Research Laboratory with funding from the Office of Force Transformation (OFT). The payload of the TacSat-1 is essentially the radio used on an EP-3 surveillance aircraft.
The TacSat-1 spacecraft was supposed to go up with SpaceX Corp.’s Falcon-1 vehicle this past spring, but it failed to launch. At the time of this writing, the relaunch for the TacSat-1 is expected for the end of this year or early next.
• TacSat-2’s payload includes a panchromatic (color and gray scale) imager and three-color capability. TacSat-2 is led by and almost entirely funded by AFRL. It is currently going through integration, which is expected to be completed June 30. There is a source selection underway for the launch. Wegner expects it to launch within about a year.
• The TacSat-3 has a hyperspectral imager—similar to what is being developed for UAVs like Global Hawk systems. TacSat-3 is moving to Critical Design Review for the payload and the bus. The spacecraft bus itself is just going on contract. Launch is expected for fall 2007.
TacSat-3 is led and funded by AFRL, with additional funding from OFT and Army Space and Missile Defense Command.
• The TacSat-4’s payload is essentially a UHF communications transponder— solely a communications payload, as opposed to imaging. The payload is similar to that of the Mobile User Objective System (MUOS), a large communications satellite, except the TacSat-4 will have far fewer communications transponders on board.
Given their imaging payloads, TacSats 1, 2 and 3 are low earth orbit—about 450 km. “The closer you get [to the earth], the less time you last on orbit because atmospheric drag starts to take over and you burn in,” explained Wegner.
TacSat-4, however, will have a 12,000 km elliptical orbit, meaning it’s about 12,000 km at its furthest point away from the earth and about 400 km at its closest point. “Since it’s a communications payload, you want those to be fairly high so you’ve got a good field of view,” he said.
TacSat-4 is being executed by the Naval Research Laboratory, and funded by a joint partnership between ONR and OFT. Wegner estimates a mid-fiscal year 2008 launch.
Wegner emphasizes that being small, the TacSats are less capable than the big spacecraft systems being flown today. “We’re spending on the order of $50 million putting a TacSat into orbit. You can’t do the same thing on that kind of platform that you can do on a platform you’re spending billions of dollars on. It’s in some sense like a UAV. You can’t do as much on a little Predator as you can on an F-15 platform, for instance. But there are niches for both, and that’s really what we’re trying to explore.”
Though having similar payloads as those of UAVs, TacSats would have certain advantages over UAVs. One such advantage is that missions could be carried out over denied areas and/or in secret.
However, TacSat orbits can not be changed. So it would be difficult if not impossible to get an already-launched Tac- Sat over an area of interest that is not already directly beneath its existing orbit.
But one of the tenants of responsive space is that a TacSat could be launched very quickly in order to place it in the right orbit. “We can essentially tailor the orbit to pass over that spot on the earth a number of times—maybe as many as four to six times a day, depending on where it is.” Wegner said. With a small constellation of these—perhaps five—an area could be observed almost every hour of the day.
A constellation of the TacSat-4, which will have a highly elliptical orbit, will enable 24/7 communications coverage over a particular location.
ANGELS REPAIR WORK
In a separate development from the TacSat program, the AFRL Space Vehicles Directorate has awarded three competing contracts for the preliminary design of a nanosatellite (which will be closer to around 20 kg) capable of independently providing localized space situational awareness (SSA) for a host satellite. The contracts, awarded in March, went to SpaceDev, Boeing and Lockheed Martin.
The program is known as Autonomous NanoSatellite Guardian for Evaluating Local Space, or ANGELS.
Air Force Lieutenant Luke Sauter, Deputy of the AFRL Space Superiority Office at Kirtland AFB, explained that an ANGELS nanosat would be launched together with a host satellite. In addition to demonstrating a working nanosat with communications with the ground, the main purpose of the experiment will be to facilitate maintenance and repair of the host satellite. The nanosat would be able to back off some distance from its larger counterpart, and provide photographs of the exterior of it, in cases of suspected malfunctions or damage to the host.
The ANGELS would be its own freeflying satellite, not tethered to the host satellite. It would initially be hooked up to the main satellite on launch, and then as commanded from the ground, it would detach and operate independent from the host. Even if the host is completely dead, the nanosat would provide residual capability to figure out the problem. That being said, Sauter notes that it does not last too long outside of the host.
Ideally there will be two modes of operation, he explained. Either it could watch the deployment of a satellite, because a lot of failures on orbit occur as satellites are starting to deploy, after which time it would be disposed of. The other mode of operation is keeping it attached to the host until there is some sort of problem, at which time it could be detached.
Another concept is to have its sensors always on, even when it’s attached, in order to always watch for any kind of anomaly on the host spacecraft.
“About 50 percent of the satellite anomalies that we’ve run into are some kind of external failure or can be attributable to some external event that can be seen,” he observed. Many such anomalies occur with solar plates, such as solar panels failing to deploy, which in turn may cause a power failure. “If you had another pair of eyes on orbit to actually see what has happened, you have an advantage of trying to figure out some way of bringing your spacecraft back online or trying to figure out some work-around.”
The size of the nanosat is not finalized, but AFRL is shooting for a mass of about 20 kilograms.
Sauter emphasizes that the functionality of the nanosat will be limited. For example, it will only provide still photographs, not video, due to its low data-rate communications. And it will not be able to carry out repairs—only provide situational awareness. In addition, it will not provide tactical functions, such as enemy satellite detection.
It will be in a geostationary orbit— about 36,000 km high—for experimental purposes because this is a more stressing environment, in part due to higher levels of radiation.
The Preliminary Design Review is expected for the end of July, and the Critical Design Review is set for May of 2007. “Ideally we’d have delivery of the satellite system in December of 2008,” indicated Sauter.
SpaceDev’s $1.25 million contract requires that the nanosatellite be capable of flight by early 2009. It is to have a one-year mission life, with a goal of three years for its operational life. SpaceDev will carry the design to a Preliminary Design Review level, and has the option to carry it to a Critical Design Review level. SpaceDev’s partners include BAE Systems, Emergent, SAIC, Schafer and Vacco.
MISSILE DEFENSE MICROSATS
SpaceDev also has a contract with Missile Defense Agency (MDA) to develop a constellation of microsatellites. The company is now in the production stage of that contract, having gone through PDR and CDR. The purpose is to create small microsats that will have ground link capabilities, and that also will have what’s known as crosstalk capabilities, where the microsats can communicate with each other in space, according to Mark Sirangelo, CEO of SpaceDev. This would happen in conjunction with the larger satellites as a part of an overall scheme.
The initial experiment would be for a constellation of three satellites.
Because of the curvature of the earth, there are times where the small satellites might not be able to link to a ground link station. So the ability to connect with microsatellite number 1, which in turn could communicate with satellite number 2 and number 3, would expedite the ability to be responsive to its space situation, explained Sirangelo.
“The idea is that to be able to be fast and responsive, and not put all of the military’s assets into one device,” said Sirangelo. And [the microsats] are a lot more portable and easy to get up there, and more efficient to operate. If there’s a problem in a certain area, you could deploy more rapidly to provide supplemental coverage to that area.”
SpaceDev aims to launch the MDA microsats within two years. Once the program is well established, the process of launching a new satellite could be done in a matter of months, not years.
Microsatellites certainly will not replace conventional satellites. Commented Sirangelo, “The goal is to be able to have the wider range of more distributed abilities— part of a complete system that provides sensor and information to military and government.” ♦
