Interplanetary Transports

[Dizzle]

So I'm generally not very ambitious, and my interplanetary missions have been imprecise to the point where they barely make it. Today I had the idea to build a ship specifically for interplanetary transit. The idea was to make something with large crew and fuel capacity. It would be sent between planets, with stations that are already there to perform orbit-to-ground work, and vice-versa. After some time in the VAB, I launched Space Bus.

screenshot26b by dizzle229, on Flickr

It was surprisingly easy to get into orbit, which I thought would be the major hurdle. I've yet to send it anywhere, but I can already predict some problems.

1. Every body needs a fuel station to keep the wheels on Space Bus going round and round. In addition, every fuel station needs to be refueled itself.

2. Very long burn times. Even with four LVNs, this thing doesn't get close to 1G of thrust. I fear that since a transfer burn would have to be performed over multiple passes, it might end up at a stage where it's at Kerbin-escape-velocity, and not enough time left to complete the burn in the right position. Slapping on some higher-thrust engines means sacrificing ISP, and even now it only has about 10 km/s Delta-V. Not sure how much the external tanks will add to that.

3. Going off of the last one, slowing into orbit around bodies. With such low thrust, is it even capable? That 10 km/s may sound like a lot, but I don't want to try aero-braking this thing.

This thread isn't so much about this particular craft as it is about the concept, the problems inherent in the concept, and hopefully, solutions. Have you guys tried something like this? Is it worth the trouble? I've always seen people building motherships and wondered how they'll fare when they have to aero-brake.

[Guest]

If you have 10km/s you should be able to get from Kerbin to anywhere and back, you just might need to wait for a better window. So long as your TWR is at least 0.25 you should be able to do a single burn to anywhere (well, except maybe Moho to Eeloo or something). Your space-bus is just fine for ferrying crew from Kerbin to anywhere and back, well done.

[mikegarrison]

This thread isn't so much about this particular craft as it is about the concept, the problems inherent in the concept, and hopefully, solutions. Have you guys tried something like this? Is it worth the trouble? I've always seen people building motherships and wondered how they'll fare when they have to aero-brake.

Yes, I build them all the time. Usually if I'm playing with stock parts, I stick a couple of the biggest Kerbodyne tanks together and run three or four LV-Ns. I stick a clampotron Sr. on the front and this not only gets me to other planets and back again, but also serves as the orbital fuel tank for a planetary lander. I can tag Duna, come back up, cruise over to Ike and land there, and then go home again.

The big problem is the low, low TWR. Usually I build my landers such that I can fire their engines too, if I need extra thrust. But you can climb out of the gravity well in steps, too. Just don't try burning all at once from a very low orbit, because that causes problems.

Aerobraking is no problem. That's probably not realistic, but then again this is KSP....

But now I am experimenting with the Near Future nuclear reactors, and that works much better! A couple of big reactors, a couple of big electric engines, some huge (but light) liquid hydrogen tanks, and I have a interplanetary mothership that has something like 30,000 m/s delta-v (with lander attached!) and still has better TWR than the LV-N versions did. The main drawback here (in career mode) is that each ship costs close to 2M to launch. So you need a lot of cash to build up a fleet of them.

Edited April 18, 2015 by mikegarrison

[DMSP]

I love IPVs (Inter Planetary Vehicles)!

Glad to see another person with some. Yours looks great!

I'll post a photo of my most recent one and my design for my next 15.

Don't ask why I have so many, let's just say that my CPU was down for 2 months.

[KerikBalm]

May I suggest that you make it a 2 stage craft (coupled with docking ports, not decouplers).

Stage 1 can have more thrust, and it just boosts you to kerbin escape velocity + a little more.

Once stage 1 has acheived kerbin escape velocity (maybe through use of PE kicking, maybe not) - and then maybe a couple hundred m/s more (depending on the remaining fuel in stage 1)

-disconnect it, and have it do a retroburn to keep in in the kerbin system, then lower its PE to aerobrake back into LKO.

Your space bus then needs only a small burn to reach Duna or Eve... although its still going to take quite a bit of burning to get a Jool intercept.

Sure... you still won't be burning really close to PE the whole time, and you waste some dV due to Oberth... but you'll also make large efficiency gains by ditching some empty tanks and engines in Kerbin's SOI

[Scotius]

My last Interplanetary Transport Vessel SPace for 14 Kerbals, 10 000 + m\s dV and decent thrust thanks to engines made by Porkjet (which makes them legit IMO )

[panzer1b]

If you have 10km/s you should be able to get from Kerbin to anywhere and back, you just might need to wait for a better window. So long as your TWR is at least 0.25 you should be able to do a single burn to anywhere (well, except maybe Moho to Eeloo or something). Your space-bus is just fine for ferrying crew from Kerbin to anywhere and back, well done.

My recent batch of ION SSTOs all have roughly .25TWR and they are able to 1 shot burn to anywhere ive ever tried (even eeloo but you need to start from a higher parking orbit). Basically with the right starting orbit (not straight from LKO), id guess even a 0.2 TWR craft would be able to get anywhere in 1 burn.

The only issue low TWR for me is landing on moons and planets, unless my jet engines work (laythe and kerbin), its not exactly a craft thatll be able to land safely on anything with gravity higher then the mun.

[Dizzle]

My last Interplanetary Transport Vessel SPace for 14 Kerbals, 10 000 + m\s dV and decent thrust thanks to engines made by Porkjet (which makes them legit IMO )

Ooh, I like that. Pretty and capable.

[Norcalplanner]

http://i.imgur.com/4un1U9A.png

My last Interplanetary Transport Vessel SPace for 14 Kerbals, 10 000 + m\s dV and decent thrust thanks to engines made by Porkjet (which makes them legit IMO )

That nuclear light bulb is a thing of beauty. :-)

[magnemoe]

My interplanetary transport.

Uses an landing can as cockpit as it also act as tug so I need an 2.5 port in front.

Here its docked with an depot, spaceplane below. Carry life suport for an very long trip but that is more to resuply bases. Ship can land on Duna or Val,

To the right an heavy tug,I uses this to do the first 1km/s of burns, the tug then tops up the ships tanks and return to LKO to be refueled.

This also give extra TRW in the first phase of burn as KerikBalm suggests, one way trips to Eve or Duna hardly need much of an upper stage

Edited April 18, 2015 by magnemoe

[Renegrade]

Here its docked with an depot, spaceplane below. Carry life suport for an very long trip but that is more to resuply bases. Ship can land on Duna or Val,

I like the look (esp around the engines) but ugh.. the TAC_LS container disease kinda ruins the front :C

I really wish TAC_LS had better container support (longer inline tanks with configurable ratios, higher density radial attachment, etc).

[magnemoe]

I like the look (esp around the engines) but ugh.. the TAC_LS container disease kinda ruins the front :C

I really wish TAC_LS had better container support (longer inline tanks with configurable ratios, higher density radial attachment, etc).

Thanks and yes I agree, I should have made an cargo hold and put it in it. This way it might even been an replaceable module, all the tac containers was an last minute addition then I found the Jool base needed resupply.