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As of yesterday 01 October 2015, a team is hoping to raise £600k (~$911k) to fund a Moon impactor via Kickstarter, which should cover the costs of building and testing a two-stage rocket, a spacecraft with what seems like a custom propulsion subsystem, and a small titanium dart which should impact the Moon.

Their feasibility study seems quite imprecise and amateurish to me. Maybe are aerospace engineers not the targeted audience despite the purpose of the document being to "outline the technical requirements for reaching the mission goal and present a starting point for ongoing research and development."

How complete and technically feasible is the information presented in the feasibility study?

Below are some extracts which seem imprecise or even incorrect to me. I have added a short comment, which may be very wrong, so please correct me if needed.

Section 6.1

The trajectory from LEO towards the Moon is known as a Hohmann Maneuver, by which the spacecraft transitions from LEO to an elliptical orbit, intersecting the trajectory of the Moon.

An Hohmann transfer is one of the many different trajectories to go from one orbit to another. In actual operations, these transfers do not use the exact theoretical definition of these orbits (due to orbit corrections after adequately ranging the spacecraft while in transit).

Section 6.3

LEO altitude must be high enough to limit drag-induced altitude loss, e.g. 200 km.

To start with, what is the inclination and eccentricity of this parking orbit, then we can talk about the three other orbital parameters which are independent from time (i.e. all but the true anomaly)? If the vehicle is in such a low orbit for only a very limited amount of time before heading on towards the Moon, drag is not much of a problem in itself.

Section 7

Spacecraft shall utilize non-cryogenic propellants, as the expected nominal mission time will otherwise result in excessive propellant boil-off.

Depending on the materials used to insulate the fuel tank, boil-off can be completely negligible for most months-long missions, or am I completely mistaken?

I haven't read the full feasibility study, so I'm sure there are many passages I would question in the rest as well.

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    $\begingroup$ The Technical Designer/Developer is one of the co-founders of Copenhagen Suborbitals; so there is definitely some experience there, but you should note that Copenhagen Suborbitals has not yet achieved suborbital spaceflight, much less orbital flight followed by a transfer to Moon impaction. $\endgroup$ – called2voyage Oct 2 '15 at 19:31
  • $\begingroup$ Eh, for the passages you cite, that's about the level of (im)precision I'd expect for a "feasibility study". $\endgroup$ – Chris Oct 2 '15 at 20:34
  • $\begingroup$ Whatever the level of this study, I'd like to see their turbopumps. $\endgroup$ – Deer Hunter Oct 2 '15 at 21:25
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    $\begingroup$ With no other costs than launch costs, and the best promise of SpaceX coming true for their Falcon Heavy reusable, they might hitchhike as secondary payload on some other mission to the Moon, a mass of about 50 kg. I suspect that some people misuse Kickstarter for fraudulent purposes. One million dollar would be nice to have. $\endgroup$ – LocalFluff Oct 3 '15 at 1:19
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First of all, in direct response to your questions:

  1. A Hohmann Maneuver is a perfectly acceptable orbit transfer to get to, say, another planet. From Earth, it doesn't make as much sense to use. I wouldn't expect them to state the exact orbit, but they should have some margin for corrections.
  2. 200 km is the lowest orbit to stay at for any length of time. I think the orbital lifetime there is measured in days, at most. Personally, I would aim for higher, say, 250 km at a minimum, to give some margin. In fact, they have a chart that shows the minimum length in orbit is about 50 hours, which is indeed what I expected.
  3. Cryo fuels haven't been used for longer than a day.

It seems a bit optimistic, but not unreasonable, as a whole.

Skimming the proposal, I don't see any serious flaws. Of course, a detailed study would be required to really identify if it is capable of doing what they say they can do.

There are some issues to worry about, however.

  • What I'd be most worried about is the low margin in the power system. A 10% margin is not very much, considering they have no method of recharging the batteries. They do correctly indicate there is a 10% margin on the worst case time to achieve the mission.
  • The thrust levels are very nominal, I personally haven't seen such even levels. It might be possible (I'm more familiar with Solid rockets than liquid), but...
  • They also don't cover anything about thermal issues, which for a potentially 5 day mission could be problematic.
  • I don't see any requirements on attitude control, other than it is required. This could cause a number of problems, from transmission back to Earth, to not getting the correct attitude for firing the thruster, and likely others.
  • The navigation system could work, but I'm not quite convinced. They have the Earth, Sun, Moon, and IMU. They will be able to correctly identify the attitude if they can get the Earth, Moon, and Sun all at once, then use the IMU if one of the 3 is missing. They definitely need a breakdown on the accuracy of the sensors. The Moon might be difficult to build a sensor to detect, because it has radically different lighting and temperature values. In particular, I'm concerned that they don't seem to be using the sensors until after they do their TLI burn.
  • A COTS GPS doesn't work above a certain altitude/speed, due to anti-SCUD laws. Amateurs have previously build such a device that was capable of receiving GPS from orbit, with special permission. Still, some kind of specialized GPS system is required (And GPS probably isn't needed that much anyways).

It might also be worth comparing this to the Fox-1 project, an Amateur produced satellite, built by volunteers.

Bottom line, I think they could almost get close, but I can't see this mission happening in a short order of time. For their budget, they probably won't get the testing required to make it really sound. In particular, the thermal testing would probably cost a significant part of the entire budget, and with such a variety of thermal situations to manage, I don't think this would happen.

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    $\begingroup$ Other issues you might want to highlight: use of COTS GPS in space as a waste of mass/power, unarticulated high-gain antenna pointing accuracy reqs (I haven't done the back calculation from their stated link budget). You have nailed it re: lack of testing with this level of funding. At least they'll have enough ethanol... $\endgroup$ – Deer Hunter Oct 2 '15 at 23:28
  • $\begingroup$ I actually did highlight the lack of pointing requirements, but good thought on the GPS. $\endgroup$ – PearsonArtPhoto Oct 3 '15 at 0:57
  • $\begingroup$ Thanks for that answer and the direct responses to my questions. $\endgroup$ – ChrisR Oct 3 '15 at 1:27

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