Ask Tildes: Design a spacecraft! You've been offered to submit a space exploration misson, with a cost cap of $1 billion. What is your proposal?
You've been asked to submit a proposal for a space exploration mission of your own desire, to the New Frontiers spaceflight program. These missions have a cost cap of approximately $700 million to $1 billion, and have famously produced the following spacecraft:
- New Horizons, a flyby probe to Pluto.
- Juno, a polar orbiter of Jupiter.
- OSIRIS-REx, a sample return mission to a rocky asteroid.
- Dragonfly, a drone lander to Saturn's moon Titan.
These are medium-sized missions in both scope, and cost. You can't build the Mars 2020 Rover, or the James Webb Space Telescope. What do you send, and where? Things to consider:
Technology Readiness Level
Administrators are less likely to choose your mission if you choose to integrate risky or untested flight hardware, or novel concepts into the mission design. You're more likely to get selected with more conventional hardware.
Power Source
Your best bet is probably solar panels, maybe something commercial off the shelf like NG's Ultraflex panels? The downside is that these are only effective up to about Jupiter's orbit, and generate power according to the inverse square law. How much do these cost and weigh? How much energy do you generate?
If you go further out into the solar system than that, you'll need a Radioisotope Thermoelectric Generator (RTG). There aren't many of those around, in fact, after Mars 2020 has taken its RTG, there's two left. What makes your mission deserving of an RTG? Is there enough power in the MMRTG to power your mission?
Propulsion
Does your mission need in-flight propulsion? Either for orbit insertion, landing, or maybe a long coast with Ion thrusters like Dawn? If the latter, you can get some pretty good Xenon-powered thrusters, like NEXT, which gives you 236mN of force from 7kW of input power (this rules out an RTG as your power source).
Don't need long-term burn capability? Maybe a COTS bipropellant engine like LEROS is your thing. Watch your weight though, bipropellants aren't efficient! Often more than half the mass of large spacecraft can be dedicated to just propulsion alone.
Instruments
Go crazy. What are you looking to research? Do you need a long range camera, a wide angle camera, something outside of the visible spectrum, a spectrometer, ground-penetrating radar? Do you have a mass-budget in mind?
Launch Vehicle
Every dollar you save on your launch vehicle, you get to add to your mission profile. Your best bet in terms of performance and cost is probably Falcon 9, which retails for $62-90 million, depending on the amount of assurance for success you need. Of course, if you can find a cheaper launch vehicle, feel free to pick it if it fits into your mission weight.
Objectives
What scientific questions do you want to answer? What are you interested in exploring the most?
Alright so I am hilariously late to this party BUT I am here and that is what counts.
So with "only" a billion dollars, I think it's safe to rule out all but the most limited of manned missions, and definitely nothing that needs you to develop a new launch vehicle. However, I recently worked on a class project that I thought was interesting.
The premise was to get a ground penetrating radar (GPR) instrument close enough to the Moon to get data on locations where GRAIL gravity data and topography patterns indicate that there might be lava tubes under the surface. The secondary goal is to characterize the dark rock of the Lunar mare in terms of surface coverage and overall volume. The lava tubes are especially interesting since they may provide spaces that could be good for future manned habitation of the Moon. Within the cover of a lava tube, radiation is significantly reduced, and the thermal extremes of the Lunar surface are mitigated. Lava tubes also exist on Mars (we think), and on the Earth (we know), though they are much smaller due to higher gravity and differing geology. The lava tubes on the Moon are thought to be on the scale of hundreds to thousands of meters in width, and kilometers in length, so there would be plenty of room inside if that turns out to be true.
The project proposal we developed was aimed at NASA's SIMPLEx secondary mission program, with a cost cap of $55 million dollars (though we broke through that!). For this, I would want to do the mission for maximum science return, rather than on a budget.
So this mission would still include an orbiter, but with a few changes. It would be in a low Lunar orbit similar to the LRO to get good data return from the GPR. Of course the location of the periapsis would be moved to be over the mare, maximizing the quality of the data in that region. The orbiter would be much larger than the ESPA class smallsat we used in class, and would include both a LIDAR instrument to get confirmation on the height of the surface and a camera to take high resolution photos of the surface. There would be additional communications hardware on the orbiter that can serve as a relay for surface missions, which will come in handy for the rover I have planned. The orbiter also serves as a command and service module for the rover during transit.
Though the orbiter would be scaled up in this scenario, the rover and its new technology is where the bulk of the money would be spent. There are several locations on the Lunar surface where there are "skylights," or places where we think lava tubes have collapsed a little bit. One of these skylights would be the target for the rover. Using a skycrane style landing mechanism, a two part rover would land in the skylight.
Part one would be the base station, and may not necessarily be mobile. This part would contain power generation, likely solar panels, as well as communications to relay back to orbit.
Part two contains the science instruments and is definitely mobile. Its job is to take rock samples and photos of the lava tubes to gain more information about them. It has an umbilical back to the base station for power and communication, since if it goes into the lava tube there will be no sunlight, and carrying a RTG on a mission like this seems unlikely. Depending on final cost, this may get descoped to a solar powered lander and a rover which is powered by primary batteries, but I think with a billion dollars it should be possible to get an umbilical developed.
In terms of propulsion and mission plan, things are pretty standard here. A direct, Apollo style transfer is in order, since we don't have any special mission requirements like GRAIL did to need one of those fancy ballistic lunar transfers. Hopefully we can get a Falcon Heavy type launch vehicle to toss us on a Lunar intercept trajectory, from there capture as well as station keeping for the orbiter and landing for the rover should be something that a conventional hypergolic propellant like hydrazine can handle. Might need to be a bipropellant depending on mass and cost constraints, but of course I'd have to do the engineering to know.
And most importantly, every mission needs a name! I think Hestia would be a good name for the overall mission, since that is the Greek goddess of the home and hearth, appropriate for a mission that could be finding a Lunar home for humanity. Naming the individual spacecraft would probably use variations on hearth and fire, since those are Hestia's symbols.
I think the precision landing and use of the umbilical are definitely the biggest technical and mission risks. However, because of the environment, I don't really think there is a cheaper or safer way to get inside the lava tubes and collect data. Whether or not doing that is strictly necessary is another question, but I think it is cool at the very least :)