DOW-UAP-D143: Laser Lightcraft Nanosatellites

Source file: DOW-UAP-D143_AAWSAP-DIRD-Laser-Lightcraft-Nanosatellites-November-1-2010.pdf Originating agency: Defense Intelligence Agency (DIA), Defense Warning Office, Advanced Aerospace Weapon System Applications (AAWSA) Program Document type: Defense Intelligence Reference Document (DIRD), "Defense Futures" series; control number DIA-08-1011-001 Date: 1 November 2010 (information cutoff date, ICOD: 30 August 2010) Classification: UNCLASSIFIED//FOR OFFICIAL USE ONLY (the FOUO caveat is struck through on every page; released to the public in 2026) Page count: 77 VIRIN: 260918-D-D0360-1132 PURSUE Release: 6

Summary

This DIRD asks whether very small satellites could be put into orbit cheaply by a vehicle that carries almost no fuel and is pushed instead by a powerful laser on the ground, at sea or on an aircraft. The cover gives the date 1 November 2010, an information cutoff date of 30 August 2010 and the control number DIA-08-1011-001, under the heading "Defense Futures". It was "Prepared by" the Technology Warning Division (DWO-4), Defense Warning Office, Directorate for Analysis, DIA, and the author is given as "AAP Person 58", the same pseudonym that appears on DOW-UAP-D142, the quantum-vacuum DIRD. The administrative note calls it "one in a series of advanced technology reports produced in FY 2010" under the AAWSA Program and directs questions to "AAP Person 1", the AAWSA Program Manager, at a DIA address in Washington, D.C. (PDF page 2). A box on the same page describes the DIRD format as providing "non-substantive but authoritative reference information."

The paper has a two-page summary and five chapters: nanosatellite technologies; Lightcraft propulsion; a "weapon mission selection study"; a review of multi-megawatt lasers; and a conclusion. It has 36 figures (many are photographs of flight tests and lasers credited to the Air Force Research Laboratory, the Directed Energy Professional Society, IPG Photonics and the Naval Postgraduate School), 5 tables and 35 references. Much of Chapters 2 and 3 summarizes a single earlier Air Force study by Froning and Davis (reference 26), and the swarm concepts in Chapter 3 are credited to "research notes, lectures, and briefings" from I. Bekey.

The document does not mention UFOs, UAP or unidentified aerial phenomena. The nearest phrase is a stated "military need for 1.0 kg to 2.0 kg nanosats with optical sensors for visual inspection of unknown objects in space and on Earth" (PDF page 34), which concerns inspecting objects with small satellites.

Research Article

Why tiny satellites

The summary defines the classes: minisatellites of 100-500 kg, microsatellites of 10-100 kg, nanosatellites below 10 kg and picosatellites of 0.1-1.0 kg. "The primary reason for miniaturizing satellites is to reduce cost," it says (PDF page 5), and it lists missions small craft can do that big ones cannot: low-data-rate communication constellations, formations that sample many points at once, and in-orbit inspection of larger satellites. It envisions 100 or more nanosats released from a "mother ship", each built for no more than $500k, some carrying imaging and radio instruments for "remote sensing measurements (MASINT) or surveillance and eavesdropping (SIGINT)."

Chapter 1 (PDF pages 7-14) is an engineering checklist. It sets thruster requirements (total impulse 3,000-7,000 N-sec, a specific impulse of 280 seconds), a command-and-data computer of 0.25 kg and 0.5 W, and a radio of 0.5 kg at 8,470 MHz. It works out that a disk-shaped nanosat 0.3 m across would generate only 4.0 W from its solar cells, and that twelve AA-size lithium-ion batteries weighing 480 grams would carry it through an eclipse. It compares three thermal designs, whose internal temperatures fall by about 60, 20 and 6 degrees Celsius during an eight-hour shadow. Parts of this chapter read like a civil science mission: spin-stabilized craft in highly elliptical orbits, "particles and fields instruments", a "science mission attitude" perpendicular to the ecliptic, and repeated references to "scientific or intelligence" data. Its key proposal is that the laser that launches a nanosat should also supply the thrust it needs in orbit, so the satellite carries only small attitude thrusters (PDF page 7).

Riding a beam of light

Chapter 2 explains the Lightcraft. The vehicle looks like "a fat acorn": a pointed forebody, a ring-shaped shroud, and a highly polished parabolic mirror underneath. A ground-based infrared laser fires kilojoule pulses 25 times a second; the mirror focuses each 18-microsecond pulse into a ring inside the shroud, where the air breaks down into a plasma of 10,000 to 30,000 K and the resulting shock wave pushes the craft along the beam (PDF pages 16-17). In the design developed at the Air Force Research Laboratory (AFRL) at Edwards AFB, the craft breathes air in this way up to Mach 5 and 30 km altitude, then switches to a "laser thermal rocket" mode, using the beam to heat a small onboard propellant. The paper traces the pulsed air-detonation idea back to the German V-1 "Buzz Bomb" engine of the Second World War.

The history section gives the actual test record (PDF page 17). The program began under the Strategic Defense Initiative Organization in the late 1980s; in the 1990s NASA's Marshall Space Flight Center and the AFRL propulsion directorate flew prototypes at the High Energy Laser Systems Test Facility at White Sands Missile Range using the U.S. Army's 10 kW PLVTS carbon-dioxide laser. A Lightcraft reached 43 m in 2-second vertical flights, flew 121.9 m along a horizontal guide wire, and a later series reached 38.7 m; a private communication reported 68 m. The author compares this to Robert Goddard's first liquid-fuel rocket, which reached 12.5 m in March 1926, and adds: "In sharp contrast with Goddard's rockets, there is absolutely no fuel on board the prototype Lightcraft, which has a diameter of 10 cm, mass of 20 to 40 g, and is machined from a solid block of 6061-T6 aluminum." Reaching orbit would need a megawatt-class laser, at least 100 times more powerful than the one used in the tests.

The claimed benefits are large: single stage to orbit, fully reusable, payload fractions of about 50-95%, a specific impulse that is "essentially infinite" while breathing air, launch costs "two to three orders of magnitude" below existing ones, "$20/kg to $600/kg of payload", and a need for 0.1 to 1 MW of beam power per kilogram of vehicle (PDF page 21).

What the Air Force study found

The core evidence is the Froning and Davis study for AFRL. For payloads of 10, 5 and 1 kg, Lightcraft takeoff masses came out about 45, 80 and 360 times smaller than rockets, and transport costs about 3, 5 and 15 times lower (PDF page 23). A ground laser at 1.62 micrometres, radiating 10 MW through a 10 m aperture, could lift an 8 kg Lightcraft and put about 4 kg in orbit (PDF page 24). The study assumed air-breathing flight up to Mach 10, twice the Mach 5 given for the AFRL concept a few pages earlier.

The study also found the physics unforgiving. As the craft climbs and moves downrange, the beam has to cross more atmosphere at a steeper angle, ending about 83 degrees from vertical at roughly 500 km range. Beam spreading and the atmosphere together cost "on the order of 75% to 99%" of the radiated power (PDF pages 25-27). The best wavelength, 1.62 micrometres, belongs to the free-electron laser, whose demonstrated power was then about 20 kW, so a "500-fold increase" would be needed (PDF page 27). Table 1 puts a 10-year program of 1,000 launches a year, each carrying 2.0 kg, at $741.4 million, of which $624.8 million is the 10 MW ground laser. It quotes "$74,141 per flight" and "$3,052" per kilogram, but the table labels the per-kilogram figure as based on operations costs only; spread over its 2 kg payload, the per-flight figure is about $37,000 per kilogram (PDF page 29).

Choosing a mission: satellites yes, weapons mostly no

Chapter 3, the "weapon mission selection study", reports that "the most promising Air Force mission" is placing Earth- and space-observing nanosats of up to 3 kg in low Earth orbit (PDF page 31). The craft would double as a "Lightsat": its propulsion mirror becomes a telescope and its forebody panels unfold as solar arrays, so only 0.1 kg of its 1.0 kg dry mass is reserved for satellite functions. Tables 2 and 3 compare a three-stage hybrid rocket weighing 715-921 kg with a Lightcraft of 2-20 kg, and give cost ratios of 16.82, 4.67 and 3.00 in the Lightcraft's favor for 1, 5 and 10 kg payloads over 100 flights. The per-flight Lightcraft costs in Table 3 include laser power and refurbishment but no share of the laser's purchase price, and the paper itself warns that more detailed comparisons are needed "before a strong argument can be made for either design" (PDF page 34).

Weapon uses get a mixed verdict. Tables 4 and 5 compute that a 1 kg Lightcraft flying at 3 km/s into a head-on collision with an ICBM warhead travelling at 6 km/s would strike with 81 MJ. The tabulated energies equal mass times closing speed squared; the standard kinetic-energy formula, one-half of mass times speed squared, gives half as much, about 40 MJ in this case. But beam-riding times are long, clouds interfere, and the lasers and aircraft are expensive, so "no truly attractive Lightcraft combat mission was found" (PDF page 33). A few pages later, the same chapter says air-launched Lightcraft "show much promise" for intercepting missiles above the atmosphere and could eliminate jamming satellites, citing the 2001 Rumsfeld Space Commission (PDF pages 37-39). The two statements sit side by side without being reconciled.

The chapter ends with swarm concepts in which thousands of tiny satellites act as one enormous antenna or telescope: a radio collector 20 km by 40 km made of 150,000 picosats of 23 grams each, which "can receive sub-watt signals from individual cell phones"; two radiometry swarms; a radar of 10,000 one-kilogram nanosats radiating 3 GW peak from geosynchronous orbit; and a hyperspectral sensor with a 100 m Fresnel lens on a 100 km tether, resolving 40 cm from geosynchronous orbit (PDF pages 41-45). For the radar, the paper concedes that "specific performance calculations have not been done for this concept." The paper says the swarms "probably can be demonstrated by 2015 and deployed in space by 2020." Nearly every one comes with a note that its mass could fall a hundredfold "if Buckytubes are used", meaning carbon nanotubes.

Finding a megawatt laser

Chapter 4 reviews a 2002 study by V. Hasson of TEXTRON Systems, which recommended a 10 MW electron-gun-driven laser running on a nitrogen, carbon dioxide and hydrogen mixture: four 2.5 MW modules pulsing at 125 Hz, with a 300-second run consuming 72 metric tons of gas, at an installed cost of about $230 million (PDF pages 46-50). From this design the paper calculates that one 2.5 MW module could send 5.25 kg to orbit for $2,793 in electricity and liquid gases, or $532 per kilogram, "41 times lower" than the "$10,000 per pound" of chemical rockets. It notes that this excludes operations, life-cycle and maintenance costs (PDF page 51).

The rest of the chapter surveys newer lasers: Northrop Grumman's solid-state slab laser, which produced almost 106 kW in early 2009, DARPA's 150 kW HELLADS, fiber lasers of 50-70 kW, and a Navy free-electron laser design of 2 MW. It predicts megawatt-class solid-state output "within three to five years" and fiber lasers scalable to "1 to 2 MW beam power within 1 to 2 years". It admits that "no detailed Lightcraft nano- or pico-satellite payload launch cost estimates can be performed at this time", then offers a "back-of-the-envelope" $100-$300 per kilogram, or $800-$2,000 with all costs (PDF page 66). A section on beam control describes new directed-energy-weapon pointing systems and says ground launch will need mirrors of about 10 m.

Conclusions and caveats

The conclusion restates the claims and ends with a recommendation. It notes that AFRL ended its Lightcraft program in 2005 "before launching a Lightcraft test vehicle into LEO was demonstrated", that the Air Force Office of Scientific Research was then funding a Brazilian Air Force shock-tunnel study with Leik Myrabo's group at Rensselaer Polytechnic Institute, and that "this author" recommends the Department of Defense and NASA "return laser Lightcraft propulsion R&D to the United States" (PDF pages 73-74).

Readers should keep several caveats in mind. The launch-cost figures quoted in the paper span two orders of magnitude, from $20 to more than $3,000 per kilogram, depending on what is counted. The prototypes actually flown weighed 20 to 40 g, and the test laser limited designs to about 60 g, against the 2-20 kg vehicles in the tables. Much of the case rests on one Air Force study and on laser power levels that did not yet exist. The paper does not explain how a beam this powerful would be kept safe for aircraft or satellites along its path, beyond mentioning "safety systems" and budgeting for FAA and NORAD coordination in Table 1.

Significance

Among AAWSAP's 12 technical areas, this DIRD belongs mainly to propulsion, with a mission study that touches armament (kinetic interceptors) and supporting topics such as space surveillance. It is one of the most conventional papers in the series: beamed-energy launch is established, if unrealized, aerospace engineering, and the flight tests it describes are backed by AFRL photographs and published papers in its reference list. It shows AAWSAP's reference library reaching well beyond exotic physics into near-term space access, and it pairs naturally, by subject, with DOW-UAP-D137 on high-energy lasers and DOW-UAP-D124 on space access in the same release. The same "AAP Person 58" label appears on DOW-UAP-D142, which suggests that one contributor wrote on both beamed-laser engineering and quantum-vacuum theory. It offers nothing on unidentified phenomena.

Key People

Locations

Key Concepts

Notable Quotes

"The primary reason for miniaturizing satellites is to reduce cost." -- page 5

"In sharp contrast with Goddard's rockets, there is absolutely no fuel on board the prototype Lightcraft, which has a diameter of 10 cm, mass of 20 to 40 g, and is machined from a solid block of 6061-T6 aluminum." -- page 17

"Unfortunately the demonstrated laser beam power levels for the attractive 1.62 µm wavelength, which suffered the least propagation losses, are relatively modest." -- page 27

"It was concluded that the most promising Air Force mission for a laser-propelled Lightcraft is the placement of Earth and space observing nanosats of up to 3 kg mass into LEO." -- page 31

"Thus, no truly attractive Lightcraft combat mission was found." -- page 33

"There is a military need for 1.0 kg to 2.0 kg nanosats with optical sensors for visual inspection of unknown objects in space and on Earth." -- page 34

"The technologies to produce these swarms and their constituent nanosats or picosats probably can be demonstrated by 2015 and deployed in space by 2020." -- page 41

"No detailed Lightcraft nano- or pico-satellite payload launch cost estimates can be performed at this time because the high-power solid-state and FEL laser devices are emergent technologies still under development and testing; operational deployment is expected to take place within the next two to five years depending on near-future funding and programmatics." -- page 66