In sci-fi movies, like Independence Day, we find one big mothership flanked by many small droneships.

Take-off and landing giant spaceship is technically difficult and dangerous. The landing surface may be uneven and not too hard for touch down.

Like ISS, the mothership can be assembled in space, using smaller spaceships, and these docked reusable droneships can be deployed for landing on the moon, Mars and even Earth. Is this proposal of mine has more flaws or much more practical?

  • $\begingroup$ Your question makes assertions that are not supported by evidence, and your edit adds more. The bit about launch clamps is frankly just weird, there's no reason to think they're necessary. SpaceX is experimenting as much with pad construction as with the Starship prototypes, occasional damage is to be expected. There is nothing to indicate that Raptors are hard to cluster, no planned version of Starship even mounts 12 Raptors, and the lunar version has separate landing thrusters. And Falcon 9 is one of the larger launch vehicles in operation, but is still too small for practical full reuse. $\endgroup$ – Christopher James Huff Nov 24 '20 at 3:32
  • $\begingroup$ Is it much concern in the amount of "damage" we do to a Lunar or Martian surface? $\endgroup$ – corsiKa Nov 24 '20 at 3:35
  • $\begingroup$ @corsiKa there's some concern about the debris that would be kicked up and what it might do to other vehicles, equipment, or habitats. Of course, by the time you have such things to worry about, you can set up prepared landing pads. $\endgroup$ – Christopher James Huff Nov 24 '20 at 3:44
  • $\begingroup$ I am a big SpaceX fan and eagerly waiting for Starship to take-off. Question has been edited. $\endgroup$ – seccpur Nov 24 '20 at 5:29
  • $\begingroup$ Either ship is going to need landing gear, the landing gear of a bigger ship will simply be a bit more complex than that of a smaller one. $\endgroup$ – Mast Nov 24 '20 at 7:45

The idea is good, but I would argue that the technology isn't there yet. Ignoring the (big) problem of orbital debris, you would need good automated docking technology for small vehicles. Some companies, like Astroscale from Japan, are working on docking technologies for spacecraft refueling. Such technology needs to be mature enough before we can do large scale automated assembly in space. Another option would be using technology soon-to-be demonstrated by the "Made In Space" company where structures are 3D printed on orbit.

Combining on-orbit printing with on-orbit assembly would allow us to build very large structures without the constraint that these structures need to survive launch and subsequently correctly deploy on orbit.

  • $\begingroup$ Decent answer +1 for 3D printing in space. $\endgroup$ – seccpur Nov 24 '20 at 0:24

Uneven surfaces are easier to handle for larger landing craft, since the variation is proportionally smaller compared to the vehicle itself. A Falcon 9 booster requires a pretty much flat surface, a Starship should be able to handle as much as a couple meters of variation. If you need to land a vehicle that's less capable, you can land something else first and prepare a landing site for it.

You've brought up launch clamps before. It isn't clear to me why you think they're necessary. SpaceX has done several flights of Grasshopper vehicles and Starship prototypes with no launch clamps.

Splitting a vehicle into a mothership and subcraft has numerous downsides:

  • Subcraft and motherships require you to develop, build, and operate two vehicle types instead of one.
  • Subcraft are dead weight the mothership must haul around for much of the trip.
  • Subcraft represent dry mass that must shuttle back and forth to deliver payloads to/from the mothership. If they must make multiple trips, this can add greatly to the propellant requirements.
  • The mothership must stop in orbit at the destination. It is possible for this to be done with aerocapture, but this requires much more precision in atmospheric braking than simple entry and landing does, and also requires the mothership to have most of the thermal protection and aerodynamic features it would need to land. It is likely you will burn more propellant getting the mothership into orbit than you would landing it.
  • The penalties of reuse are proportionally larger for smaller vehicles. Things like heat shielding will be a larger part of the overall mass budget. Gauge issues mean there will be more structural overhead for smaller craft. For example, directly scaling down sheet metal components might lead to the sheet metal being impractical to build with, requiring you to use heavier sheet metal than would theoretically be necessary.

There may be an argument for such a split if the mothership is of extremely large size (far larger than Starship) and makes use of exotic propulsion systems not compatible with landing (such as nuclear-electric propulsion), but the advantages will have to outweigh the numerous disadvantages, and such a vehicle isn't going to be a replacement for Starship.

  • $\begingroup$ Isn’t huge motherships when this is proposed? I was imagining something on the scale of an O'Neill cylinder 8 by 32 kilometers. Then the smaller ships could be the size of dreamliner or maybe skylon. $\endgroup$ – lijat Nov 24 '20 at 10:14
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    $\begingroup$ And yet, we landed on the moon with a drone ship (LM) and had a mothership (CSM) in orbit. $\endgroup$ – Polygnome Nov 24 '20 at 11:08
  • $\begingroup$ @Polygnome the moon ship had one significant less drawback to contend with, the atmosphere of the moon is basically non-existant. So no heat shielding of neither LM nor CSM was necessary. $\endgroup$ – Prof. Falken Nov 24 '20 at 12:32
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    $\begingroup$ The Apollo CM returned to Earth, it wasn't an orbital "mothership". Apollo was a minimalist approach to getting to the lunar surface, and the requirement of doing an entirely propulsive landing, the low amount of payload they were actually delivering, and non-reusable nature of all the hardware involved meant it was easier to leave the return craft in orbit and stage off both the lander and ascent modules, and discarding them as soon as they'd done their jobs. Mars has an atmosphere that does most of the work of braking for landing, and Starship is fully reusable. $\endgroup$ – Christopher James Huff Nov 24 '20 at 15:18
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    $\begingroup$ @Polygnome multiple trips with a smaller craft is an extremely inefficient approach, on top of the greater propellant costs of entering orbit instead of directly landing. You're burning lander craft loads of propellant for every trip to unload the mothercraft, and more to load it again, shuttling the dry mass of those landing craft back and forth between orbit and the surface multiple times while hauling payload with vehicles that have a lower payload fraction. And Starship is likely close to the lower size limit of a fully-reusable launch system. $\endgroup$ – Christopher James Huff Nov 24 '20 at 17:19

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