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According to aerospace engineer James Longuski of Purdue University in Indiana,

We can go to Ceres as easily as Mars

The key technology that a human mission to Ceres needs to develop is a nuclear power plant capable of generating nearly 12 megawatts of power.

Still, the investigators said that even without these options, their work demonstrated that a human mission to the dwarf planet was feasible.

Is this true? Is going to Ceres "as easy as going to Mars", or does different technology need to be developed for going there other than the technology used for going to Mars?

Ceres Asteroid Solar System Space Science

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    $\begingroup$ In Ceres: A prime target for robotic sample return and future human exploration, K. R. Fisher and L. D. Graham argue that a human mission (with return) to Ceres would be easier than would be a human mission (with return) to Mars. $\endgroup$
    – David Hammen
    Feb 14, 2020 at 14:27
  • $\begingroup$ Neither the 2012 proposal by Laipert and Longuski (which prompted the National Geographic article) nor the 2019 proposal by Fisher and Graham (my previous comment) has attracted much attention. The problem isn't technological ease so much as doing so would mean (at least temporarily) surrendering the decades (centuries?) long dreams of sending people to Mars. The huge emotional investment in that dream gets in the way of more realistic endeavors in space. $\endgroup$
    – David Hammen
    Feb 14, 2020 at 15:04
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    $\begingroup$ SpaceX is pursuing a plausible way to get to Mars and back with methalox chemical propulsion, using engines that have already been developed to the point of flying test platforms. Longuski proposes development of a 12 MW nuclear electric propulsion system to reach Ceres. One of these is not "as easy as" the other. $\endgroup$
    – Christopher James Huff
    Feb 14, 2020 at 17:01
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    $\begingroup$ it could be read another way - at the moment. "We can go to Ceres as easily as Mars, which is to say, as easily as a pig can put on pants and pilot an airplane to Greenland, which is to say...not at all" ;) $\endgroup$
    – NKCampbell
    Feb 15, 2020 at 2:19
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    $\begingroup$ @Christopher James Huff: Of course that depends on whether you consider SpaceX's (and other proposals I've seen) to be "plausible" as far as human living conditions go. In any case, going to Mars really isn't the big problem, it's getting back that's the hard part. It's a lot easier to build an ascent vehicle to get from Ceres surface to the orbit where you've parked your ship, than to do the same for Mars. $\endgroup$
    – jamesqf
    Feb 15, 2020 at 7:35

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This hinges as bit on what "as easy as" means. We clearly can't go to Mars today because we don't have the technology. We do have all the bits and pieces in theory, but we haven't build anything that can actually do it. SpaceX is famously trying to do exactly that with Starship/BFR.

The discussed paper is Low-thrust trajectories for human missions to Ceres. Frank E.Laipert, James M.Longuski (Published in Acta Astronautica Volume 95, February–March 2014, Pages 124-132). We can find in the conclusion:

5. Conclusion

We can draw the following conclusions from this mission design study.

  1. A human mission to Ceres could be made feasible with the appropriate investment in propulsion and in-space power technology. Given the assumptions used here, the total IMLEO, with a 10% margin, would be 458 Mg. The mission architecture presented here would deliver a total of 155 Mg of payload to Ceres over two missions. Four heavy-lift launch vehicles would suffice to carry out such a mission.

  2. Nuclear electric propulsion technology enables human exploration at Ceres because it has a relatively low specific mass (i.e. about 5 kg/kW) and it avoids a costly impulsive capture maneuver at Ceres. Electric propulsion technologies capable of processing input power up to 11.7 MW (or more) should be further developed to open the possibility of exploring Ceres.

  3. Total mission times of less than 2 years (for the crew) are possible with nuclear electric propulsion. In the absence of a proven method of blocking deep-space radiation, limiting mission times is the best way to limit the danger to the crew.

So the point is, its easy if we have that power source.

Still, the investigators said that even without these options, their work demonstrated that a human mission to the dwarf planet was feasible.

Hm, what I found is:

4. Discussion

4.1 Key technologies to develop

The primary technology enabling a human mission to Ceres is a nuclear power system capable of generating 11.7 MW of power with a specific mass of 5 kg/kW. A mission may be feasible with a smaller power system of around 8–9 MW, however more propellant and a higher IMLEO would be required. In addition to the power system itself, an electric propulsion technology capable of converting that power into thrust with an efficiency of about 70% is needed. (highlight mine)

That doesn't seem to confirm this statement.

That being said, I don't think the statement "We can go to Ceres as easily as Mars" is too misleading. Delta-v to intercept mars is about ~4300 m/s from LEO, for Ceres its more like ~4500m/s (doing some back-of-the-envelope math), that is not to far off. You can not aerobrake on Ceres though, which makes landing a lot harder, but launching is also easier. The problems faced are certainly different.

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  • $\begingroup$ Those are one-way delta V costs to Mars and Ceres, with the Mars delta V postulating aerocapture, a technology that has remained at the TRL 1 to 2 level (i.e., ideas on a piece of paper) for decades. Then you have to add the cost of EDL, which is high and complex for Mars, cheap and simple for Ceres. Finally, to avoid being classified as a murderer, it's a good idea to account for costs of launch and return. $\endgroup$
    – David Hammen
    Feb 14, 2020 at 14:37
  • $\begingroup$ Aerocapture is unnecessary: every Mars lander has done direct descent and landing, landing far more payload in the process than would be possible with a purely propulsive spacecraft of the same size. The EDL systems they've used to do so have been far cheaper and simpler than the 12MW nuclear-electric propulsion system proposed for Ceres. $\endgroup$
    – Christopher James Huff
    Feb 15, 2020 at 15:02
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Well, I'd say that "We can go to Ceres as easily as Mars" isn't quite true, but it's really a matter of perspective.

On the one hand, measuring by fuel expenditure, specifically rocket delta-v, a journey to Ceres would be rather similar to a journey to Mars. The difference in delta-v requirement to go to Ceres is only around 400 m/s more than going to Mars according to this solar-system Delta-V map. A rocket that's capable of preforming a propulsive capture and landing on Mars would be able to do the same thing on Ceres. Essentially, if we have the technology to go to Mars, then going to Ceres wouldn't be a problem.

On the other hand, going to Mars may be cheaper or easier than going to Ceres as Mars' atmosphere allows aerocapture or aerobraking maneuvers which greatly reduce fuel costs. A spacecraft which is designed to aerocapture into Mars orbit may not have enough fuel to propulsive capture into Ceres orbit.

I think that when James Longuski says "We can go to Ceres as easily as Mars" they're talking about the technology level required to preform such a mission, not the actual price. Nothing new needs to be invented to send humans to Ceres if Mars missions are already on the table.

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    $\begingroup$ A Mars mission takes about 5-6 km/s of propulsive delta-v for departure and 1 km/s landing. Ceres, if using high-thrust engines, takes 6.4 for departure and another ~6 on arrival. With a specific impulse of 380 s (the Raptor engine), that's a propellant mass ratio of about 7:1 for Mars, 26:1 for Ceres. A Ceres craft could do propulsive capture and a fully-propulsive landing on Mars, but no Mars mission would ever do that. This would be the reason the study authors proposed nuclear-electric propulsion systems and two craft that each deliver a capsule-sized spacecraft. $\endgroup$
    – Christopher James Huff
    Feb 15, 2020 at 15:41

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