DARPA wants to put real-time links into tiny satellites

The military has been working on developing small, inexpensive satellites for short-term, specific uses, but a key to making them work is fitting high data-rate capabilities into small form factors without enough power to do the job.

The Defense Advanced Research Projects Agency has begun the solicitation process for lightweight and low-power inter-satellite communications links for nanosatellites, or CubSats. DARPA wants to “provide the highest data-rate between microsatellites, consistent with their small size and limited power consumption.”

More specifically, DARPA wants to go as small as possible with the most output. “[T]his program seeks to develop [inter-satellite communications links] with the highest practical data rates while having a per-link average weight of less than 2 pounds and an orbit-average power dissipation of less than 3 watts,” the solicitation states. “Efforts proposed under this BAA will explore link concepts and demonstrate revolutionary flight hardware that yields ISCLs with high communication data rates (>1 Mbps) within very tight weight and power constraints. Both optical and radio frequency (RF) links will be considered.”

The proposal calls for development in two technical areas. The first, requiring development within 24 months, calls for the links to be able to operate for at least a year. The second, independent of the 24 month schedule, is aiming for more “aggressive enabling technologies and higher performance system[s].” 

These microsatellites will be procured with the intention of conducting intelligence, surveillance and reconnaissance (ISR), which means that they should be survivable and require jam-resistant communications. Additionally, they will also serve as communications systems and therefore must require, at the very least, near-real-time data capabilities.

DARPA requires a nominal communications range of between 2,000 and 4,000 kilometers (roughly 1,200 to 2,400 miles).    

Microsatellite capabilities have come in demand recently, since they can potentially serve myriad purposes for relatively little money. The Navy is looking into similar technology that could hitch a ride into orbit with larger satellites and, once deployed, could extend the range of satellite communications or be used in support of a specific mission.

The Army also has sought to utilize nanosatellites as a means of achieving “over-the-hill” battlefield communications as well as bolstering communication coverage to soldiers in areas that typically do not receive reception. 

From tracking ships on Earth to potentially providing Internet coverage, nanosatellites’ low cost and low-Earth orbit pattern – approximately 1,200 miles altitude on the high end – can provide for increased signal strength than satellites in more farther reaching orbits.  

DARPA listed major technical challenges for its program as follows:

• Achieving the highest possible data rates within the tight weight and power constraints described above. This will entail getting high energy efficiency per-bit on each link, by optimizing transmit gain, receive aperture, transmitter power efficiency, receiver sensitivity, losses, and using energy-efficient waveforms and coding. Standby and static power dissipation of the system will also need to be minimized.
• Providing lightweight mechanical or electronic (e.g. phased-array) means to point the ISCL beam, antenna or optics toward a target satellite to acquire and maintain the communication without interfering with the host satellite operations.
• Having a robust approach for link acquisition with a desired neighboring satellite, and for maintaining that link. PAT and link maintenance can be particularly challenging for optical links, with their narrow beam widths. Proposals must address how reliable PAT and maintenance of links will be achieved.
• For Technical Area 1, being able to have the ISCLs fully developed, tested, and ready for integration onto an experimental satellite within 24 months is also expected to be a challenge.

 The response date is Aug. 3, 2015.