Introduction

On November 21 1994 Jordin T Kare presented a rocket concept called “Mockingbird” while working at the Lawrence Livermore National Laboratory or LLNL. This is a video about that but first, context about what led up to it.

SDI

On March 23, 1983 Ronald Reagan announced the Strategic Defense Initiative, or SDI program which had a goal of allowing the US to intercept and destroy ballistic missiles before they reached America or its allies. To do this he called upon America’s scientific community to make nuclear weapons obsolete [1]. Among the designs to do so included lasers and anti-ballistic interceptors to destroy incoming missiles [2].

The interceptors eventually became what is now known as Brilliant Pebbles, a concept for thousands of satellites that were small, cheap, mass produced, and smart to impact nuclear bombs that were recently launched. For replenishment and testing of the satellites a very small rocket that could launch a single Brilliant Pebble on demand could be quite useful [3].

ASTRID

The Advance Single-stage Technology Rapid Insertion Demonstration, or ASTRID, was built to demonstrate the feasibility of a small, high-velocity interceptor vehicle, which could be launched from a unmanned, high-altitude aircraft which was Responsive Aircraft Program for Theater Operations, or RAPTORS [4, 5].

 It launched on February 4, 1994 out of Vandenberg Air Force Base by LLNL. This was a single stage vehicle powered by a hydrazine liquid rocket engine. This engine had its propellant pressurized by reciprocating piston pumps powered by the decomposition of the fuel into ammonia, nitrogen, and hydrogen after passing through a catalyst. ASTRID demonstrated piston pumps were viable in flight and attractive for small propulsion systems due to their high thrust to weight ratio [6].

From ASTRID, TALON, short for Theater Application Launch On Notice would be derived [7]. If ASTRID was launched from RAPTOR it would have accelerated in excess of 2 km/s, enough to get to space, which TALON was designed to do [8]. TALON missiles were to be launched from a RAPTOR aircraft to intercept missiles in boost phase on the opposition’s turf, likely in a more horizontal direction than going as vertical as ASTRID. I can’t find a good source for what exactly TALON would be powered by, but it seems like it would use dinitrogen tetroxide, hydrazine, and or hydrogen peroxide. The RAPTOR and TALON programs were canceled around 1993 similar to Brilliant Pebbles. In 1995 the Scaled Composites Raptor Demonstrator was transferred to NASA as a flying testbed [9].

MOCKINGBIRD Overview

Amidst these developments, Jordin T. Kare got a contract by the Department of Energy which caused him to publish 43 very interesting slides on a concept called Mockingbird, a Multiple Application Rocket Drone [6]. Also from my understanding there were probably more powerpoints and papers than the one I’m referencing but they never left the inside of LLNL.

Mockingbird would be a single stage rocket hopefully able to get to low earth orbit. Its dry mass would be between 45 and 110 kgs with a wet mass above 1500 kg from its nontoxic storable hydrogen peroxide and kerosene, propellants which have environmentally benign combustion products. The vehicle being between 80 or 100 cm in diameter and 5 meters tall the size was chosen for the vehicle to be as small as possible as practical to have a positive payload.

Tanks

Mockingbird would have an aft cylindrical fuel tank and a fore conical oxidizer tank. They would share a bulkhead, which would either be an aluminium dome, with lower mass and less usable volume, or composite sandwich plates, with higher mass and more usable volume.

Steel, aluminum, or composite materials were considered for the propellant tank walls and structure. Aluminum was the baseline for the design, steel being heavier but needed less thermal protection, and for composite materials liners for peroxide compatibility were considered to be too heavy. The aluminium walls would be 20 mil thick, IE 0.02 inches or 0.508 mm thick which is on par with the Centaur upper stage [10]. A spherical COPV storing helium would pressurize the propellant tanks to around 2 atmospheres.

Thermal Protection System

The small nose radius made ascent thermal protection a serious problem, so the propellant tanks would either be covered with carbon aerogel on the nose and silica aerogel on the rest of the cone or cooled with an active internal spray of propellant. The carbon aerogel on the nose might be disposed of once the vehicle is in space, perhaps to allow for the payload bay to open.

Mockingbird would survive reentry through use of a 2.5 meter diameter extendable parasol of a heat resistant fabric keeping the reentry heating max temperature at 1250 k. Finally airbags would deploy cushioning the 15 m/s impact.

Engines

Reciprocating pumps that pressurize the propellants would be driven by either decomposed hydrogen peroxide or heated helium.  If heated helium was to be used then the helium would be taken from the same tank that would pressurize the  tanks to keep them in tension. The helium was to be heated by decomposed peroxide in a heat exchanger with the hot steam and oxygen flowing into the engines and the helium vented after use. The vented helium would give an ISP of over 200 seconds, but the plumbing and heat exchanger was noted to be a potential area of concern.

If hydrogen peroxide was to power the pumps only a small amount of it would be pressurized to 136 atm by smaller self powered pumps and fed through a gas generator. The high pressure hot gasses created would then power the main fuel and oxidizer pumps which would share a common shaft. All outputs from that pump would be 68 atm and go to the engines. Due to pressure drops in the pipes, coolant channels, and injector the chamber pressure of the engines would be 61 atm with an alternative version at 47 atm. This heat would cause the fire, and fire would heat the cooling channels [11].

The engines would be regeneratively cooled with pumped hydrogen peroxide and would have its chamber made of a hydrogen compatible metal. Hydrogen peroxide compatibility ruled out molybdenum. Aluminium with a thermally protective hard anodized alumina layer on the inner shell and a brazed aluminium-silicon eutectic outer shell was the baseline. Tantalum was proposed due to it being very robust, however it would be heavier and more expensive. Stainless steel also was proposed due to being intermediate in properties between tantalum and aluminium. The hydrogen peroxide would flow through etched or machined channels in the engine’s inner shell. 

The vehicle’s low expansion engines would have an expansion area ratio of 22.5 while its singular high expansion engine would have an expansion area ratio of 150. The smaller low expansion engines could be small enough to be manufactured on a small lathe due to them being 8.8 cm in diameter and around 35 cm long. The nozzle extension on the high expansion engine could be made built into the rest of the engine, or in parts that were put together to allow them to be manufactured in small separate pieces.

At sea level the 8 low expansion engines would have a specific impulse of 238 seconds, and in vacuum 301 seconds. The high expansion engine would have a specific impulse of 327 seconds in vacuum. There would also be hydrogen peroxide monopropellant thrusters derived from the TALON missile.

Hover Test Vehicle

A small hover test vehicle would test the subsystems of Mockingbird. It would use 4 of the sea level engines, propellant pumps, and an attitude control system of a full scale mockingbird. The test vehicle would have relaxed mass and stress requirements on its components. An example of this is that if the pump was to be powered by helium the helium would be stored at room temperature in an off the shelf pressure vessel and if it was to be powered by hydrogen peroxide it would use readily available 70-85% peroxide. Instead of the propellant tanks being integral with the vehicle’s wall, the tanks would be stored inside a non structural shell along with the rest of the equipment. There would also be an option emergency parachute and 1000 lbs of ballast which would not be in any way in the full scale vehicle.

Timeline

The timeline for the development program was to achieve mass production of vehicles and several flights within 3 years of starting. The timeline was to go as follows:

• In 6 to 9 months high peroxide concentration handling and production procedures would be created, the engine and pump being designed with their preliminary testing to be  started, along with finalization of detailed mass models.
• In 12 months a hover test vehicle would fly with overweight parts and simplified lower performance systems than the nominal vehicle. 
• Before year two its flight envelope would increase as its parts would get replaced by high performance and lighter ones allowing for an iterative design.
• By year two a second full scale flight weight and performance vehicle would be made and include a thermal protection system allowing for orbital flights
• In year three the Mockingbird rocket would have operational flights with production of components of the vehicle being transferred out of LLNL to allow anyone to produce and use Mockingbird like rockets along with evolution to larger vehicles.

Operations

At lift off 8 2.5 kilonewton engines would fire and at around 50 kilometers those would turn off and a single central high expansion engine would fire. Then it would maneuver with its ACS in space to the correct time, place, and velocity to deploy its payload. With the deployment finished the ACS would deorbit the vehicle and its heatshield would deploy. The vehicle would then slow down to 15 meters a second and inflate its airbags just before landing.

An accurate landing probably couldn’t be done without relighting the engines which would destroy any payload capacity. As such wherever the vehicle landed it would need to be transported back to the launch site, but fortunately was small enough to be transported by a small helicopter, a pickup truck, or if empty just two people. If refueled the vehicle could also surborbitaly fly itself there. Once recovered the airbags and thermal protection system may need to be replaced or refurbished.

Infrastructure

Mockingbird would lend itself well to minimal infrastructure. Hydrogen peroxide at 70% concentration, helium, and kerosene are commercially available fluids. Its low thrust, less than the V-2, Black Brant, and Astra’s Rocket 3, allows it to use a simple launch pad like a simple stool pod as Liberty II’s or Astra’s rocket 3 [12, 13, 14].

While kerosene can be bought in-mass, the 70% hydrogen peroxide commercially available would need to be purified, into 98% peroxide. This would be done by boiling the 70% solution into 98% through boiling away the water, likely at lower than atmospheric pressure. The hot high purity peroxide would then be cooled by a heat exchanger with liquid nitrogen and then stored in drums. 

Performance Analysis

The following is an analysis of the vehicle’s performance. The preliminary mass budget had given three numbers for the total unusable mass, 45 kg being the Goal, 71 kg considered nominal, and 107 kg considered the maximinium. I assume that there is 1500 kg of usable propellant, 1200 kg of said propellant is burned by the low expansion area ratio engines, after those stop 300 kg of propellant is burned by a single high expansion area ratio engine to allow a reasonable thrust to weight ratio throughout the flight. The low expansion engines combined produce 20 kN of thrust at sea level and 25.6 kN of thrust in vacuum. The high expansion engine produces 3.4 kN of thrust in vacuum.

The payload the vehicle can carry to a given orbit can be determined by giving the formerly stated values to the Silverbird Astronautics [15] launch vehicle performance calculator and Launcher’s [16], the company that was bought by Vast, performance calculator. Using Silverbird’s the launch site is assumed to be at the equator and final orbit a circular 200 by 200 km orbit. In the Silverbird calculator I did a simulation with the ISP of the low expansion engines with their sea level ISP and their vacuum ISP. Neither of these two values are accurate because in reality the performance would be constantly shifting. Using Launchers it can account for a shifting performance in flight as well as the option to select the vehicle diameter. 

Seen here are charts that show the calculated performance to orbit in kilograms of payloads relationship to engine performance and vehicle mass.

Silverbird	Sea level performance low expansion engines	Vacuum performance low expansion engines
Goal	17	37
Nominal	0	11
Maximum	0	0

Launcher	1 m diameter rocket	.8 m diameter rocket
Goal	18.1	25.4
Nominal	-7.6	-0.6
Maximum	-43.9	-36.6

These values should be taken with a grain of salt due to the unoptimized usage of the propellant and engines, because a custom value of how much propellant should be burned when the 8 outer engines turn off and center one turns on would increase performance. Nonetheless it makes it clear that Mockingbird would be very sensitive to weight growth, drag, and engine performance.

Evolution

The 80 to 100 cm diameter Mockingbird vehicle could evolve into larger vehicles. By evolving engines to 2-10 times the thrust. Proposed also was Mockingbird Plus or “Fat Mock” which would be 1.5 meter diameter, 10 meter high, capable of getting 100 kgs to LEO.

There were concepts for even larger vehicles, based on clustering hexagonal modules of engines with thrust chambers identical to those on Mockingbird Plus, the hexagonal modules with either 7 low expansion engines or 1 high expansion engine. These evolutions would have 300 kgs to around 3 tons of payload to LEO.

Conclusion

The Mockingbird rocket concept, developed at Lawrence Livermore National Laboratory, represents a blend of ambition and proven technology, aimed to change space access with small, cheap, and reusable rockets, simplifying space missions and reducing costs. Despite facing technical challenges, its vision for minimal infrastructure and quick launch capabilities has inspired similar concepts with interesting solutions.

Script Sources

Before I get to listing the sources there is something that needs to be made clear. As far as I can tell there is only a single primary source that actually refers to the Mockingbird, excluding an archived forum post by Jordin Kare in Fri, 03 December 1999 [17]. So if you have any information about Mockingbird that I don’t have, or realize I missed something please let me know in the comments.

Some might find Scott Lowther’s Aerospace Projects Review Blog US Launch Vehicle Projects #2 paper [18] from the pixelated preview there is clearly a Mockingbird diagram and three similarly sized vehicles next to it. Sadly the only information that Scott provides on Mockingbird is from the presentation I just cited and the three other vehicles are the Sprint Missile by Martin Marietta, GE Mk 12 Reentry vehicle by General Electric, and STAR Spaceplane [18, 19, 20]. 

1. Strategic defense initiative (SDI) (no date) Nuclear Museum. Available at: https://ahf.nuclearmuseum.org/ahf/history/strategic-defense-initiative-sdi/ (Accessed: 22 December 2024). 
2. yarchive.net, “Laser Launch,” https://yarchive.net/space/exotic/laser_launch.html [retrieved 22 December 2024].
3. Baucom, D. R., “The Rise and Fall of Brilliant Pebbles,” High Frontier (archived), https://web.archive.org/web/20230404233807/https://highfrontier.org/oldarchive/Archive/hf/The%20Rise%20and%20Fall%20of%20Brilliant%20Pebbles%20-Baucom.pdf [retrieved 22 December 2024].
4. Lawrence Livermore National Laboratory, “Science & Technology Review, July 1994,” https://str.llnl.gov/content/pages/past-issues-pdfs/1994.07.pdf [retrieved 22 December 2024].
5. UNT Digital Library, “Document 10166799,”
   https://digital.library.unt.edu/ark:/67531/metadc1340419/m2/1/high_res_d/10166799.pdf
   [retrieved 22 December 2024].
6. quantumg.net, “Mockingbird,” (archived),
   https://web.archive.org/web/20131006210340/http://www.quantumg.net/mockingbird.pdf
   [retrieved 22 December 2024].
7. Defense Technical Information Center (DTIC), “ADA338698,”
   https://apps.dtic.mil/sti/tr/pdf/ADA338698.pdf
   [retrieved 22 December 2024].
8. Snodgrass, T., “Attacking Theater Mobile Targets,” U.S. Department of Defense,
   https://media.defense.gov/2017/Dec/28/2001861682/-1/-1/0/T_0054_SNODGRASS_ATTACKING_THEATER_MOBILE.PDF
   [retrieved 22 December 2024].
9. Scaled Composites, “Raptor Project” (archived),
   https://web.archive.org/web/20180217203810/http://www.scaled.com/projects/raptor
   [retrieved 22 December 2024].
10. Defense Technical Information Center (DTIC), “AD0817380,”
    https://apps.dtic.mil/sti/tr/pdf/AD0817380.pdf
    [retrieved 22 December 2024].
11.  Yarchive.net, “Rocket Pumps,” https://yarchive.net/space/rocket/pumps.html
    [retrieved 22 December 2024].
12. AIAA, “Paper 87-1794,” https://doi.org/10.2514/6.1987-1794
    [retrieved 22 December 2024].
13. SAE, “Paper 871334,” https://doi.org/10.4271/871334
    [retrieved 22 December 2024].
14. [DARPA, “News & Events: 3 March 2020,”
    https://www.darpa.mil/news-events/2020-03-03
    [retrieved 22 December 2024].
15. Silverbird Astronautics, “Launch Vehicle Performance,”
    https://silverbirdastronautics.com/LVperform.html
    [retrieved 22 December 2024].
16. LauncherCalculator.com, “Launcher Calculator,”
    https://launchercalculator.com/
    [retrieved 22 December 2024].
17. yarchive.net, “Small Rocket Inefficiencies,”
    https://yarchive.net/space/rocket/small_rocket_inefficiencies.html
    [retrieved 22 December 2024].
18. Aerospace Projects Review, “Blog Entry #2296,”
    https://www.aerospaceprojectsreview.com/blog/?p=2296
    [retrieved 22 December 2024].
19. Defense Technical Information Center (DTIC), “ADA381863,”
    https://apps.dtic.mil/sti/pdfs/ADA381863.pdf
    [retrieved 22 December 2024].
20. MinutemanMissile.com, “GE Reentry Vehicles,”
    https://minutemanmissile.com/documents/GEReentryVehicles.pdf
    [retrieved 22 December 2024].
21. Defense Technical Information Center (DTIC), “ADB143755,”
    https://apps.dtic.mil/sti/citations/ADB143755
    [retrieved 22 December 2024].