Black Cab: A British Nanosat Launcher

Rick the Rocketeer
Preliminary thoughts on a UK nanosat launcher

Benefits of air-launch
Launch occurs above Troposphere (above the weather).
Height increase: less propellant required to reach orbit.
Air thinner at altitude: less back-pressure on the rocket nozzle improves thrust.
Launchsite infrastructure no longer required.
Can launch out at sea (lowest population density).
Launch point can be easily moved so that there is no maritime traffic at launch point or first stage impact point.
Wide choice of launch locations, can vary for launching into different orbits.
No acoustic damage to launcher from pad reflection of noise
More abort options.

White Knight 2: a gift from the Lift gods

White Knight 2: Lift
Excess lift capacity (around 17 tonnes) can carry a heavier launch vehicle with ease, which allows use of lower mass ratios per stage, which allows:
Lower energy propellants (Lox not required).
Conservative construction: improves reliability.
Simple gas pressurisation of propellants rather than pumps.
Spare mass available for systems to recover and reuse 1 st stage.

White Knight 2: drag
Launch above 50,000 feet allows:
Lower drag loss, allows much fatter fuselage (White Knight 2 can handle a fuselage up to 2.3 metres in dia).
Fatter fuselage allows more efficient tankage (more spherical), reduces mass.
Fatter fuselage allows use of lower density propellants (nitrous, ethane, propane, peroxide).
Unlike all other air-launch schemes, White Knight 2 places no volumetric constraints on the launcher.

Candidate propulsion, 1 st stage:
Moderate to high chamber pressure required.
Safety requirement: close proximity to a manned aircraft on the ground and during climb to 50,000 feet.
Use British experience with nitrous.
White Knight 2 already has nitrous conditioning hardware for Spaceship 2 (engine hot air bleed for warming the nitrous tanks).
Large multiport nitrous hybrid.
Alternatively, nitrous-ethane self-pressurising biprop (similar to very reliable XCOR ‘teacart’ engine).

Candidate propulsion, 2nd stage:
Can use low chamber pressure (space engine).
Restart capability required for orbital insertion.
No volume restrictions on tankage.
Biprop preferable for Isp and thrust-vectoring.
British experience with both nitrous and peroxide.
Nitrous-propane, gas-pressurised peroxide-propane, gas-pressurised peroxide-gas pressurised kero.

Candidate propulsion, 3rd stage
Same as 2 nd stage.
Or, use a solid.
Solid is simpler, but less accurate orbital insertion unless the previous stage does the ‘pointing’ and delta V tweaks, as the Black Arrow 2 nd stage did.

Current thinking:
There are two distinct schools of thought in the alt.space community for launching from an aircraft:
1: airdrop: drop conventional rocket from underneath or out the back of an aircraft.
2: winged: drop or tow a rocket with wings.

1: Airdrop method
Example of one of several air-launch methods currently being investigated.
Uses parachute to retard the rocket’s back-flip (retards pitch rate).
Rocket then fires from the vertical position as required.
Lightweight and simple solution.
E.g. ‘Quickreach’: 40,000 kg launch mass for 450 kg into LEO.

Airdrop method continued
Peak thrust vector control angles reduced compared to horizontal release (pegasus).
Peak dynamic pressures (max Q) reduced.
No longitudinal bending loads on airframe.
No possibility of carrier aircraft being struck by launch vehicle or its debris, because vehicle passes well behind the aircraft upon ascent.
Low tech solution.
Proposed by Tspace (carried under the aircraft) and Airlaunch LLC (rolled out of the rear aircraft door).

3 stages, all solids.
Dropped from horizontal at 39,000 ft and Mach 0.82
23,130 kg at launch for 227 kg into 400 nm sun-synch orbit.
Ratio of launch mass to payload = 102:1
2: winged, e.g. Pegasus

Pegasus continued
Dropped at high airspeed (Mach 0.82, 240 Kts IAS) due to small wing area.
High airspeed and lowish altitude (39,000 ft) gives high max Q (max equivalent airspeed).
High-speed pullup eats a lot of sky: noticable delta V loss.
Pullup is gee-limited to around 2.5 gee.
1 st stage steered by 3 movable fins only. Upper stages use thrust vectoring nozzles.
High acceleration on 1 st stage (approx 9 gee at burnout) keeps equivalent airspeed high enough for fins-only steering before staging.
1 st stage has good inert mass fraction despite wings, stiff fuselage to resist transverse lift load, and fin actuators: a good composites achievement but proves it’s do-able.

CNES/ONERA Dedalus
European rip-off of Pegasus (CNES).
3 stages, all solids.
Like Pegasus, the upper stages hang off the nose, therefore the first stage ends up very tail-heavy upon stage separation: makes 1 st stage aerodynamically unstable, so can’t glide-recover 1 st stage.
Upper stages aren’t recovered either.
Dropped at 16 Km (53,000 ft), Mach 0.7, horizontally.
15,000 kg at launch for 150 kg to Sun-synch orbit.
Ratio of launch mass to payload = 100:1

CNES Telemaque
3 stages: 2 nd and 3 rd stage within cargo bay of 1 st stage.
Cargo bay located at vehicle C.G. to minimise C.G. shift when upper stages separate.
1 st stage glide-recovered and reused.
Just over 30,000 kg at launch, for 250 kg into sun-synch orbit.
Ratio of launch mass to payload = just over 120:1
To get decent first stage delta V (3 km/sec) need very light structure (low inert mass fraction). Need to work hard to achieve this with wings and stiff fuselage.

Recover 1 st stage? Sim results:
Want around 3 km/sec delta V from 1 st stage.
Gives burnout Mach of around 10 ( if high gee ascent).
1 st stage apogee around 540 Km.
Re-entry starts at Mach 11 at 70 Km up.
Main deceleration occurs around Mach 6 at 40 Km up.
Moderate aero heating: need thermal protection (high temperature resins/carbon-carbon).
Need ballute (balloon ‘chute) or wings.
SpaceX intends recovering Falcon 1 1 st stage (not winged) from a higher delta V. Not sure how.
Similarly, Kistler aerospace proposed recovering both stages of KS1 (not winged).

Recover 1 st stage by parachute ?
Supersonic large diameter ballute as first stage of recovery (tested by NASA up to Mach 10). Stainless steel inflatable cloth bag coated in viton rubber.
Somewhat conversely, the bigger the ballute, the lower the gees and the heating. (numerous sim results).
Then main chute (gliding chute?).
Splash down in sea, just offshore if using gliding chute.

Recover 1 st stage by wings ?
Need moderately low wing-loading (= all-up mass divided by wing area) to limit re-entry gees during pull-up to near-horizontal glide.
Re-entry heating increases with square root of wing-loading.
Lower wing-loading reduces landing airspeed.
So need biggish wings.
Big wings gives drag and mass hit during ascent.
But launch from white knight 2 needs bigger wings anyway as white knight 2 max airspeed is lower than the pegasus launch aircraft.
Remotely piloted: land on land or sea?
If land on land need simple sprung undercarriage (mass penalty).

Pimp Spaceship 2!
SS2 currently gives a delta V of around 1.4 Km/sec.
If this could be raised above 2 Km/sec then SS2 would be useful as a recoverable 1 st stage.
SS2 already in development: flight testing in progress, moulds available.
Remove crew, turn into an R.P.V.
Remove cabin, replace with mid-fuselage cargo bay for upper stages.
Reduce structural safety margins slightly to save mass (no longer crewed).
Add extra nitrous tank in nose.
Re-engine with larger hybrid.
Improve thermal protection.
Just a wild thought:

Or:‘Black cab’
Combination of selected bits of Pegasus, Telemaque, Spaceship 2, Blue steel missile, and Skylon.
Potential problem of shock-shock interaction if trying to use SS2’s elevons: they might melt off at higher Mach Numbers.
Also, SS2 folds up the rear part of its wings to move the wing centre of lift forward at high angles of attack for trimming: this reduces the effective wing area, but we need all the wing area we can get.
Use canard instead, which translates fore and aft to take the trim over large angle of attack range.
Wing anhedral (negative dihedral) to increase re-entry supersonic lift to reduce gees and heating.
Re-enter at angle of attack for max lift (around 60 degrees).
Needs CFD (Cranfield?) for aerodynamic tweaking.
2 nd and 3 rd stages carried in payload bay at vehicle C.G.

‘Black cab’ preliminary sketch

Black cab launch

Re-entry

British expertise
Qinetiq and British Aerospace too big: would cost too much.
Cranfield Aerospace (docked onto Cranfield Uni, won the X43 contract).
Cranfield and Bristol Unis (Aerodynamics).
Marshalls Aerospace (Pegasus launch aircraft).
Formula One teams (composites).
Irvin Parachutes (UK).
Various UK rocket engineers.
Notable UK simulation engineers.
Airborne Engineering (engine test-stand, power systems and avionics)
Surrey Satellites.

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Black Cab: A British Nanosat Launcher

by A. Rocketeer on Nov 29, 2009

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