Thought on Moho

[Rocket Farmer]

Moho is a pain to slow down for. Has anybody ever tried not slowing down the whole ship?

Has anybody ever gotten an intercept with a mother ship and then fire a small ship off the front to arrive several days earlier than the mother ship at Moho. In those days it could slow down, land, take off, reaccelerate and dock with the mother ship as it rounds Moho?

I guess I'm asking if its even remotely possible to dock with something that's coming in with 4.5km/s relative speed?

[Pursuedtank]

Yes you could, but it's going to end up being far better to just slow down the whole ship, rather than have enough delta V in your "small lander" to reduce most of the speed, land, take off and increase the speed up so you could match orbit with the mothership. All in all your small ship ain't exactly going to be that small.

[Rocket Farmer]

Off the top of my head a kerbal, a chair, a probe, a communication array, a battery, solar panels, 1.125 tonnes of fuel, and a 24-77 rocket sitting on Moho weigh 1.3 tonnes, have a starting TWR of 1.56 and delta V of 4,315 which would come close to catching a passing return vessel.

So 1.3 tonnes on the surface isn't too bad.....

[Sof]

Off the top of my head a kerbal, a chair, a probe, a communication array, a battery, solar panels, 1.125 tonnes of fuel, and a 24-77 rocket sitting on Moho weigh 1.3 tonnes, have a starting TWR of 1.56 and delta V of 4,315 which would come close to catching a passing return vessel.

So 1.3 tonnes on the surface isn't too bad.....

On the surface of Moho no. But the mass is not down to the weight on Moho. It stays the same where ever you go, and that is the part that costs so much delta v to slow down and speed up.

Possible, sure. Better fuel economy/lower launch mass, nope.

[Horn Brain]

Since this is KSP, I say go for it and show us your pictures.

In real life, however, this wouldn't make sense unless you could detach the lander pretty close to (a few days before) your encounter with Moho. Unless you give the thing a huge kick when you do that, though, you'll only have a few hours on the surface, tops. If you're going to expect someone to survive for several days, then you need to bring along something about the size of the Apollo capsule at least.

I would say the best you could do (thinking Mercury, here) is have a small crew capsule undock from the large interplanetary habitat a few days (maybe a couple weeks, tops) before encounter, give itself a significant dV kick to give at least a day on the surface in head start time on the mothership, then perform a direct descent and landing to the surface. The ascent vehicle would be very small (think like some lawn chairs on top of a fuel tank), and would have to perfectly time the launch and boost to intercept the mothership, which would then be responsible to maneuver in close enough for either capture with a robotic arm or EVA. The savings for this system would be in not having to slow down and reboost the interplanetary habitat, as well as whatever dV could be saved by using the flyby as a gravity assist maneuver to get an encounter with Earth on the way back out. The costs would come mostly from the extra kick you'd have to give the lander in order to get a lead on the habitat, as well as the extra costs of slowing down from the non-optimized encounter by the lander.

Having thought about it, it doesn't sound so crazy after all in terms of the savings/cost analysis, and I could imagine seeing some potentially large mass savings for an actual mission, depending on lots of other parameters, like the actual mass of the required interplanetary habitat for shielding and other purposes, etc. The real problem with this plan is that there is very little time for anything to be fixed if even a single thing goes wrong once the lander leaves the habitat, and there is absolutely no backup if there is a significant delay in the ascent phase. Even in Apollo, they could have fiddled with the engines on the surface and waited for the next orbit of the CM, and the CM could come get them if they got into a bad orbit due to engine trouble after liftoff, but with this plan, there would be exactly one chance for the engines to work, and after that it would likely be impossible to reach the habitat.

Then again, I don't know the exact mechanics of the flyby. Maybe you could arrange it so that you had some extra dV in the ascent stage so that you could catch up to the habitat after a little bit of a cruise. All these things add weight, though, and cut into the savings in the first place.

The fact that there are this many considerations tells me the plan isn't totally crazy, and it may be worth a look just to get an idea of the feasibility of it. Good thinking!

[Rocket Farmer]

To Sof

My bad. That unit is 1.3 tonnes of mass on Moho. Figure with a nuke and 6 tonnes of fuel with a transfer stage a max of 8 tonnes boosting off the front of the miter ship.

To Horn

I kinda got to the same place you did. I figure with a significantly heavy starting mother ship if I prefect this I could probably land on a half dozen planets without fueling relatively easy.

As for time figuring on an 80 day Moho boost if you pick up even another 100 m/s on the mothership (which is cheap) I should get there about 2-4 days earlier which would give you some time to slow, land and speed back up. Before trying it I really am trying to gauge if you could accurately catch something going by.

A second thought was to send 2 separate ships with the second being the return vessel that doesn't slow down.

I don't know. I'll figure some more on it.

[Merinsan]

If you are flying past Moho at 4.5km/s, then you're going to need at least 9km/s delta v just for capture/landing and rendezvous, plus whatever extra you might need for landing and course corrections.

Certainly possible, but a nightmare in terms of the logistics of it.

it would be fantastic to see someone do it though.

[metaphor]

You can definitely do that, but in that case why would you even need a mothership? Why not just eliminate it altogether? By the time you've landed and re-docked with this mothership, you're already on an orbit that intersects Kerbin's, so you don't need any further delta-v to get back to Kerbin. In other words, if the lander can rendezvous with the mothership on this trajectory, it will also be able to get back to Kerbin by itself.

[Rocket Farmer]

That's a valid point.

However if you are visiting several planets the mothership can carry several of the landers and can visit all of them cheaply voyager style. Meanwhile periodically super light landers can be deployed to land as you approach the next planet.

I figure skipping eve and tylo you probably wouldn't need a lander bigger than 8 tonne for any of the rest (and you could use a single stage lander and refuel it for the low grav spots) meaning having a payload of 80ish tonne plus mothership and you could do a stock grand tour with landings without refuelings. With some more work you could probably land on all of the planets/moons.

I thought of it after I saw that a guy had done a grand tour with just a single aerospile engine and lots of patience with the intercepts.

[metaphor]

I thought of it after I saw that someone had done a grand tour with just a single aerospile engine and lots of patience with the intercepts.

Haha I think that was me. Flybys are a lot easier than intercepts though. If you have enough delta-v to get out of Kerbin's SoI and a little more for trajectory correction maneuvers, you can visit the SoI of any body in the game provided you're willing to wait long enough. Landing on them is the hard part though, you need a lot of delta-v for that. Especially Moho. I did a grand tour style thing earlier, and Moho was the one I couldn't land on without refueling. It's probably a lot easier right now, but here is what I did if you want to see it (Part 1, 2, 3).

[Joshington]

I only tried getting to Moho once. I was able to get to it, but the final burn needed to get int orbit was 20 minutes long, and was already low on fuel. So much for atomics.