Tuesday, November 29, 2016

Microsatellites - Revolution in Orbit (Chapter 1)

 I've been an observer and sometime participant in the microsatellite business since 1992, 
when I wrote my first paper on the topic.  The field grows and changes so fast it's very hard to keep up
 with the basic news, let alone all the accomplishments being logged. But where did it begin?
This is an intermittent series poking through some of the information I (and some co-authors like Erika Vadnais) have picked up in many years of looking at this topic, talking to the entrepreneurs and the engineers, and writing.  (Not included is information I/we developed on company time at our employers’ expense: companies get touchy about that.)  However, as authors of The First Space Race (NASA/Texas A&;M, 2004) (which developed out of a microsat history book project called Little Star, which we may actually get back to one of these years) we learned lot on our own time: enough to provide some historical context to a fast-moving industry.  

We'll go back to the earliest days in later installments, but I wanted to focus this time on the decade that is easily forgotten but was absolutely pivotal: the 1990s.
First. what's a microsatellite?  I like the common (but not universal) standard of 100kg or less for a microsatellite and 10 kg or less for a nanosatellite.   Back in the 90s, the U.S. Air Force (USAF) referred to “smallsats” as under 1,000kg or 500kg, either of which is hopelessly antiquated after decades of shrinking electronics and other components.  For a long time it was generally accepted a microsat would be single-string (no redundant components) and single-mission, but relentless miniaturization is slowly moving us away from those norms. 
I’m going to focus in this first segment on military satellites, because truly commercial microsatellites are a relatively recent development.  The pioneering Orbcomm UHF constellation by Orbital Sciences Corporation (OSC) (which also flew the first small booster developed in the U.S. in decades, the air-launched Pegasus) orbited its first satellite, the pioneering Orbcomm-X (or Datacomm-X) in 1991, but Orbcomm for many years had commercial microsats to itself.   
To get back to the topic, the microsat didn't emerge out of nowhere. 
The first satellites, like America's pioneering Explorer I and Vanguard I of 1958, were small because they had to be (and military because no one else had the money and expertise).  Explorer I, America’s first response to the much larger Sputniks, was built into the fourth stage of the Jupiter-C launch vehicle. The satellite portion was only 84 cm long and 15 cm in diameter.  This section was made of 410 stainless steel, its bare sandblasted surface marked with white stripes of aluminum oxide.  Explorer 1 weighed 6.35 kg on its own and 14 kg if the fourth stage of the booster (which remained attached) was counted.

An Explorer 1 model with transparent display version of front section (NASA)

As boosters became more powerful from the early 1960s on, the U.S. military moved to orbiting increasingly larger and more capable payloads. In the decade from 1978 to 1987, for example, only six military microsats were launched.  (Four of these belonged to the Navy’s Transit navigation series, which operated from 1962 through 1996.)  
Beginning in 1987, the Defense Advanced Projects Research Agency (DARPA) (known for part of its history as ARPA), led a resurgence of interest  which resulted in  military proof-of-concept satellites of the late 80s and early 90s with clunky acronym-ed names like GLOMR, MACSAT, DARPASAT, LOSAT-X, and the MicroSat constellation. The most notable one of the early 1990s was the UHF store-and-forward communications bird called MACSAT, one of which was pressed into operational use in the first Persian Gulf War.  Despite this success, the Navy's proposal for a follow-on constellation, ARCTICSAT, was canceled. For the rest of the decade, the largest U.S. military space service, the USAF, basically laughed out loud at the idea these toys could be useful.  (OK, an organization cannot physically laugh, but the Air Force came as close as possible.)

Two MACSATs stacked for launch (DARPA)

NASA never abandoned microsats completely: the Explorer series moved from its original Army home to  NASA and continues today, and the Particles and Fields Subsatellite (PFS) series put tiny satellites into orbit around the Moon from Apollo missions.  NASA entered a new era in 1995 when MicroLab-1 (later turned over to the contractor, OSC, and redesignated OrbView-1) demonstrated that a microsat could provide environmental data.  The 68-kg satellite mapped thunderstorm activity and created moisture and temperature profiles by measuring the occultation of Global Positioning System (GPS) signals received through the atmosphere.
Military communications, as well as commercial telephone, broadcasting, and other applications, was generally provided since the 1960s by large high-capacity satellites in the geostationary belt.  Microsats were not going to add much here, but there’s another way to do commemorations. Low-orbiting satellites can receive comm over a theater and downlink it to a headquarters and vice versa (store-and-forward) or provide continuous “bent-pipe" communications with a constellation of spacecraft to ensure that at least one satellite will always be in contact with the user.  Such smallsat constellations were orbited by the U.S. and the former Soviet Union beginning in the 1960s.  The concept was tested again by DARPA in 1991 when a single launch vehicle orbited seven 23-kg UHF MicroSats, creating a constellation providing continuous voice and data communication within a footprint about 5000 km wide. The entire system, including launch, cost under $20 million (M) in 1998 dollars. 
After Congress denied DARPA requests for $30M in Fiscal Year (FY) 1993 and $24M in FY 1994 requests for related projects, the DARPA "lightsat" program was essentially dead. This was despite the 1994 Air University study Spacecast 2020, which made another point in favor of such satellites.  If a large satellite has a nominal 10-year life and a microsat two years, the microsats  are able to go through five generations of technology improvement for every one generation of the largesat.  This has become more important as time and technology have progressed: every large satellite launched is essentially behind the technology curve thanks to years in preparation.  In 1998, Air Force Chief Scientist Daniel Hastings gave a strong endorsement to "smallsats."  While cautioning that “moving to smaller, distributed satellites is not a panacea for all problems,” he said, “The potential exists for really revolutionary changes in respect to moving to smaller systems.” He had no idea how right he was.
Other countries made experiments in this decade, too, and not only in communications.  One of the most interesting was France's 50-kg CERISE, launched in 1995.  This spacecraft monitored HF emissions to validate technology for a future operational signals intelligence microsat called Clementine (no relation to the U.S. lunar probe of the same name.)
The commercial world didn’t lack for pioneering entrepreneurs, but for quite a while Orbcomm was the only one that got serious traction. One of the pioneering commercial firms, predating Orbital, was AeroAstro, led by visionary/evangelist Rick Fleeter. Fleeter had no patience with approaches that just tried to shrink conventional satellites a little. He once observed that the military “thinks a small satellite is 900 kilograms. We think it’s 9.”  AeroAstro tried to shrink satellites drastically in the late 90s, marketing the 1-kg Bitsy spacecraft bus.  It was advertised as costing under $100,000 (plus payload), being customizable for applications including remote sensing, communications, space science, and technology testing, and taking nine months from ordering to delivery to a launch pad.  The vision, though, as so often happens, was ahead of the market. Useful payloads small enough and using only a few watts of electricity just were not ready yet, except for UHF radios. No Bitsy ever flew.   
One of the reasons microsats were dismissed in the 1990s was their inability to take anything but very low-resolution images.  This was considered a hard limit: the relationship between mirror size and image resolution (equivalent to the pixel size in electronic images) was inviolate. If you wanted a satellite that could spot a car (much less read the proverbial license plate), you needed a mirror diameter measured in meters.   In the 1990s, inventions like “folded optics” and the Charge Coupled Device (CCD) imager began a revolution which would lead eventually to the Planet (formerly Planet Labs) microsatellites in orbit today, in which images with three-meter resolution are taken from a satellite with a once-ridiculous aperture diameter of 10cm.      
Other advances drove miniaturization, including the reduction of computers to single chips and composite-based construction.  FORTE, a 215-kg satellite built by Los Alamos and Sandia National Laboratories and launched in 1997 to watch for the electromagnetic signatures of nuclear tests, flew the first frame made entirely of graphite-epoxy composites.  Compared to an all-aluminum structure, this reduced the weight from 64 to 42 kg.

By the end of the 1990s, the microsatellite revolution, despite halting and sometimes shaky progress, was advancing on a broad front.  Imaging, communications, electronic intelligence, weather, and other proof of concept satellites had established the potential utility of microsats, and the advance of technology – much of it in the consumer electronics industry – was enabling leaps in capability.  The stage was set for the real revolution – one that would be permanent. 

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