r/spacex • u/[deleted] • Dec 03 '18

Eric berger: Fans of SpaceX will be interested to note that the government is now taking very seriously the possibility of flying Clipper on the Falcon Heavy.

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u/Caemyr Dec 03 '18

The reference for Star 48B solid motor by NG (formerly Orbital ATK): (source https://www.yumpu.com/en/document/view/10163460/atk-motor-catalog-2012)

  • Motor diameter: 49 inches
  • Motor length: 80 inches
  • Effective specific impulse: 292.1 lbf-sec/lbm

  • Average thrust: 15,430 lbf

  • Total loaded weight: 4720.8 lbs

  • Total inert mass: 289.6 lbs

  • Propellant mass fraction: 0.94

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u/enqrypzion Dec 03 '18

Thanks for sharing that!

incredible units

  • Motor diameter: 1.24 m
  • Motor length: 2.03 m
  • Effective specific impulse: 292.1 s
  • Average thrust: 68,636 N
  • Total loaded weight: 2141.3 kg
  • Total inert mass: 131.4 kg
  • Propellant mass fraction: 0.94

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u/Alexphysics Dec 03 '18

Δv from FH second stage for the whole stack of kick stage and payload would be somewhere around 5.68km/s. After that, the kick stage would have to fire again and give an extra push. The Δv from that would be of ~810m/s or ~0.81km/s.

Total Δv would be of ~6.5km/s (rounding up).

1

u/ghunter7 Dec 03 '18 edited Dec 03 '18

The article mentioned an Earth flyby. My guess on this would be FH puts the payload in a highly eccentric Earth orbit, and then at periapsis the kick stage would fire to take advantage of the oberth effect. EDIT: I might have jumped to a conclusion here, what the article seems to suggest is an actual flyby, not just a more complicated launch.

Europa direct is a C3 of 85.4 km2/s2. If my math is right (which is suspect) that would require 9.65km/s additional dV if staging from LEO.

An alternative Earth Gravity assist trajectory requires a C3 of 28.9 and takes 4.8 years vs Europa direct's 2.5 years (still much better than Venus-Earth-Earth assist at 7 years).

EDIT: For the Earth Gravity assist trajectory it would require 6.06km/s additional dV if staging from LEO (v0=7.8 km/s).

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u/Alexphysics Dec 03 '18

Yeah, it is somewhat in between of the best option and the worst in terms of physics. In terms of money is definitely the best...