How far can you take an orange fuel tank?

[king of nowhere]

14 hours ago, camacju said:

The route was K-M-M-M-K-M-K-M-D (I bounced off Kerbin and Mun twice).

I have a question though, was all that complicated trajectory necessary? when i go to Duna, I generally do it with a single Mun assist without any problem. while i admire your gravity assist mastery, in my own experience overthinking them too much loses more than it gains

[camacju]

2 minutes ago, king of nowhere said:

was all that complicated trajectory necessary? when i go to Duna, I generally do it with a single Mun assist without any problem. while i admire your gravity assist mastery, in my own experience overthinking them too much loses more than it gains

I saved >100 m/s and it could have been >150. Correction burns are much smaller than the benefit from this path. And for going farther than Duna the benefits scale. It's almost always worth it to use gravity assists.

[Quincunx]

18 minutes ago, king of nowhere said:

I have a question though, was all that complicated trajectory necessary? when i go to Duna, I generally do it with a single Mun assist without any problem. while i admire your gravity assist mastery, in my own experience overthinking them too much loses more than it gains

I think if you do a single Mun gravity assist and burn at Munar PE for Duna, you lose out on the Oberth effect from Kerbin and therefore actually cost dV relative to a direct insertion rather than saving it. Multiple Munar GAs can be used to eject you from the Kerbin system, whence further GAs (executed like camacju did) will add to your savings.

I'm sure if you give it a try, you will confirm that a direct insertion is more efficient than K-M-D, and multiple GAs are the way to go.

[king of nowhere]

35 minutes ago, camacju said:

I saved >100 m/s and it could have been >150. Correction burns are much smaller than the benefit from this path. And for going farther than Duna the benefits scale. It's almost always worth it to use gravity assists.

strange. I could swear I got direct gravity assists to Duna just with a minimal Mun insertion, but trying it now only sent me to a 16 GM solar apoapsis, and I needed 950 m/s kerbin burn to reach Duna with a Mun assist. i guess i was wrong.

But i still could swear getting to duna with the single 850 m/s Mun injection...

still, if you eventually go on a solar orbit with a kerbin resonance, i see no particular reason why you can't do that with a single mun assist?

17 minutes ago, Quincunx said:

I think if you do a single Mun gravity assist and burn at Munar PE for Duna, you lose out on the Oberth effect from Kerbin and therefore actually cost dV relative to a direct insertion rather than saving it. Multiple Munar GAs can be used to eject you from the Kerbin system, whence further GAs (executed like camacju did) will add to your savings.

I'm sure if you give it a try, you will confirm that a direct insertion is more efficient than K-M-D, and multiple GAs are the way to go.

burning at munar PE was never the intention. I was just under the - apparently erroneous - impression that you could go directly to Duna with 850 m/s.

Re: "overthinking your assist will be bad",while i definitely admire camacju's mastery of gravity assists, and i am aware that they do save deltaV, i do not consider 44 years an acceptable time for a jool mission.

[camacju]

1 hour ago, king of nowhere said:

i see no particular reason why you can't do that with a single mun assist?

You can eject with a single Mun assist but that requires a large initial burn. Two or three assists mean that you can set up a better ejection with less delta-v expended.

1 hour ago, king of nowhere said:

i do not consider 44 years an acceptable time for a jool mission.

44 years was just due to poor planning on my part. I don't usually wait for transfer windows. I've had 200+ year missions before.

[Pds314]

On 3/20/2021 at 7:31 AM, VoidSquid said:

You're not. All dv maps I know about are not including any GA assisted trajectories, I'm sorry.

Naturally, the higher the mass, the  greater the GA effect of a given CB can be, for the Kerbol system that would be, apart from Jool, Eve, Kerbin and Duna.

I'm not entirely sure it would even make sense to talk about a GA map. A lot of it would be "you can get this orbit to that orbit for arbitrarilly little delta-V and arbitrarily high patience."

Edited March 22, 2021 by Pds314

[Quincunx]

On 3/21/2021 at 11:52 AM, camacju said:

Kerbin orbit to Duna landing took 885 m/s, Duna orbit to Laythe landing took 557 m/s, and Laythe orbit to Kerbin landing took 695 m/s.

Optimal value for Kerbin->Duna is 831 m/s, optimal for Laythe->Kerbin is 590. Not sure what optimal for Duna->Laythe is but I almost certainly lost some efficiency there also. Now that I see these numbers I definitely could have fit in a Minmus landing had I flown this mission better.

Apologies for the bump, but I just had a think, and I think Duna orbit -> Laythe surface should be possible in <400 m/s. I just applied the same reasoning as you with the Kerbin orbit -> Duna surface calculation -- you can use Ike the same way you used the Mun. I'm not sure how many Ike GAs you need, but ideally you should be able to use one or more Ike flybys to get kicked out of the Dunan SoI and then spam resonant orbits again. 360+30 m/s to get an Ike encounter, and maybe ~10 m/s to set up the multiple GAs, and you should be good. Duna->anywhere in 400 m/s.

Let's say your Kerbin orbit->Duna surface was 50 m/s more than the ideal, Duna orbit->Laythe surface 150 m/s more, and Laythe orbit->Kerbin surface 100 m/s more. That's 300 m/s, and with the 423 m/s dV you brought home, you'd have more than 720 m/s extra. According to the dV chart, it costs 860 m/s to go from Kerbin to the Minmal surface and land at Kerbin (assuming aerobraking at Kerbin to get the Minmus encounter and later AC during reentry). Darn, looks like Minmus is still just out of reach. Maybe with a better ascent from Duna or Kerbin one could save the remaining 140 m/s?

I don't honestly know if what I'm proposing is possible, but that SST Duna and Laythe with landings at both is still crazy awesome. Well done again, camacju!

[Hotel26]

I've been watching this thread, quite fascinated.

My chief impression is to wonder why people think there isn't enough challenge in KSP?  It seems gravity assists and high-energy transfers are fertile ground for moah challenge.

This has gotten me thinking about whether a slingshot via Mun on exit to get a 7-degree (Kerbol) plane change for Moho might not be a very effective tool and quite easy as gravity assists go??

[Kerbal Productions]

Hmmm... let's say the payload is a tiny Kerbal lol
If the payload is light, it COULD bring it maybe to the Mun or Minmus. Let me try.

[SpaceFace545]

I dunno if this has been said but scott manley was able to get the orange tank to duna and back.

 

[camacju]

(:

[Quincunx]

On 3/26/2021 at 9:43 PM, Hotel26 said:

I've been watching this thread, quite fascinated.

My chief impression is to wonder why people think there isn't enough challenge in KSP?  It seems gravity assists and high-energy transfers are fertile ground for moah challenge.

Glad you're enjoying it! I for one am extremely pleased with the response and participation.

Fertile ground they are indeed - but my chief impression is that you can get really good at this game if you happen to enjoy orbital mechanics calculations (which I do), so there's hope for me yet.

On 3/27/2021 at 8:22 AM, SpaceFace545 said:

I dunno if this has been said but scott manley was able to get the orange tank to duna and back.

It has been said, by me, in the OP

On 3/26/2021 at 1:07 PM, Quincunx said:

Apologies for the bump, but I just had a think, and I think Duna orbit -> Laythe surface should be possible in <400 m/s. I just applied the same reasoning as you with the Kerbin orbit -> Duna surface calculation -- you can use Ike the same way you used the Mun. I'm not sure how many Ike GAs you need, but ideally you should be able to use one or more Ike flybys to get kicked out of the Dunan SoI and then spam resonant orbits again. 360+30 m/s to get an Ike encounter, and maybe ~10 m/s to set up the multiple GAs, and you should be good. Duna->anywhere in 400 m/s.

Let's say your Kerbin orbit->Duna surface was 50 m/s more than the ideal, Duna orbit->Laythe surface 150 m/s more, and Laythe orbit->Kerbin surface 100 m/s more. That's 300 m/s, and with the 423 m/s dV you brought home, you'd have more than 720 m/s extra. According to the dV chart, it costs 860 m/s to go from Kerbin to the Minmal surface and land at Kerbin (assuming aerobraking at Kerbin to get the Minmus encounter and later AC during reentry). Darn, looks like Minmus is still just out of reach. Maybe with a better ascent from Duna or Kerbin one could save the remaining 140 m/s?

I don't honestly know if what I'm proposing is possible, but that SST Duna and Laythe with landings at both is still crazy awesome. Well done again, camacju!

I had another think (thinks are easy to have when first you take your mind off things!) and it occurs to me that there is another aspect that can be optimized. For a landing on Minmus with a spaceplane rather than a rocket, one doesn't actually need to come to rest before landing. This saves some dV and suggests the following pipe dream:

1. From an encounter trajectory, perform an orbital insertion burn around Minmus, then deorbit and use brakes to slow down. (Standard procedure)

2. After orbital insertion, instead of deorbiting, burn to lower PE to the surface of Minmus, then use brakes to slow down more. (Is this commonly done? It seems harder but appears to use less dV)

3. Instead of orbital insertion, encounter Minmus with PE just above the surface of Minmus, and burn once to an almost-circular orbit with PE on the surface. (Only one burn and dumping fuel in the gravity well - sounds good, but also harder still)

4. (Unrealistic?) Encounter Minmus with PE just below the surface of Minmus, and use only brakes to slow down. (Landing on Minmus for 0 m/s dV?!)

I sincerely doubt KSP has brakes that can decelerate from a Minmus escape trajectory to orbital velocity at the surface. What I think is more realistic is this:

4*. (Less unrealistic) Encounter Minmus with PE just below the surface of Minmus. Use only brakes to capture into an elliptical orbit, and make multiple passes until velocity is below orbital velocity at surface.

I think 4* will be the most fuel-efficient way to land on Minmus (heck, and Ike for that matter). At the risk of getting carried away, let's say we have 700 m/s dV to spare, assuming near-perfect execution of all burns and GAs. In camacju's mission plan there is already an Ike encounter (assist). If the above "tangential lithobraking"-type strategy is realistic, we can land on Ike for ~0 m/s dV. Taking off and getting back to Duna's SoI will cost (390+180+30) m/s = 600 m/s dV, whence you can escape Duna's SoI using camacju's strategy. We still have 100 m/s left over for corrections.

I think it is possible to take an orange tank to land on Duna, Ike, and Laythe while having encounters with Jool, Vall, Tylo, and Eve. That would be an incredibly difficult mission, though.

Thanks again for answering my questions and participating; this has been very informative - and entertaining!

 

[camacju]

The problem with that is that if you're above orbital velocity you won't be able to slow down much because centripetal force will exceed gravity so you won't get any traction. A more realistic and still efficient option would be to get into a suborbital trajectory right above the flats, cancel vertical velocity, and brake to a stop there.

Edited March 29, 2021 by camacju

[camacju]

Ok, I'm going to do this mission again. I made the craft slightly more efficient.

On runway

Ascent

Climb

Leveled off

In orbit with >5200 m/s of delta-v left

[camacju]

Mun transfer burn, 1 of 2

Mun assists to Minmus

Minmus encounter

Minmus capture burn

Suborbital

Saved 70m/s of wheel braking

Burning to orbital speed on the flats

In orbit of Minmus - almost 4k delta-v left. Next stop will be Eeloo probably

[camacju]

Mun transfer to 1:1 resonance with Kerbin. This is a pretty high energy transfer so I can eject with a lot more radial velocity than normal

Swing around Kerbin and Mun again to intersect Eve's orbit

Mun assist

Eve assist

After another Kerbin assist I arrive at Jool, where I use a Tylo assist to reduce Jool relative velocity

Jool is in a very bad place for a good Eeloo transfer so I encounter Jool again where the planes of the orbits intersect

Tylo assist

Jool close pass

Setting up second Jool-Tylo assist

Eeloo encounter

Landing burn

Landed with some assistance from wheel braking again

 

[camacju]

Ascent from Eeloo

Jool transfer

Laythe encounter

Aerobraking. The landing gear extension means that the plane adopts a strong nose down attitude, which is good for slowing down quickly.

Because of the inclination from the Eeloo transfer, I had come down a bit south of the equator, so I'm turning north to land as close to the equator as possible.

Landed on Laythe. I landed within 10' of the equator which is pretty good

Laythe ascent. I take a different and more efficient ascent path since I start from a lower elevation.

I try to level off at 23 km but the plane is too light for its wing area at this point so I can't be as efficient as possible.

I turn on the nuclear engine at 1730 m/s and the rapier cuts out around 1800.

In Laythe orbit, with >1000 m/s left.

Laythe escape burn

Tylo and Laythe assists

[camacju]

Tylo flyby

Laythe flyby

Kerbin encounter

Kerbin aerocapture

KSC is in the wrong place so I do a boost-glide trajectory to skip around Kerbin

Final reentry

Approaching KSC

Landed

 

Mission summary:

Landed on Minmus, Eeloo, Laythe before coming back to Kerbin

Flybys of Mun, Eve, Tylo, Jool

I think this has conclusively proven that taking a single orange tank to any body other than Tylo and Eve is possible. I highly doubt that an Eve landing will be possible with just one orange tank, same with Tylo.

[Quincunx]

And with that, you have authoritatively answered the titular question of this thread. Thank you!

[camacju]

I realized - there's actually one more destination that needs to be addressed: Moho. And the margins might be really tight. I might actually need to stage some parts off for the required delta-v.

Assume I have 5200m/s in LKO since that's what I had last time, 840-850 m/s to Mun transfer, assume 850 - 4350 m/s left

Kerbin-Eve-Kerbin-Eve-Moho gravity assist chain - 1050 m/s to capture using deep space maneuvers and Moho gravity assists- 3300 m/s left (This might be an overestimate. Last time I did this strategy I encountered Moho's orbit at a bad point in the orbit. Likely this will be better if I encounter Moho at periapsis)

Moho orbital velocity at this point is 1050 m/s, so assume 1150 m/s to land and 1100 m/s to take off

Then 1050 m/s to get back to Eve and then back to Kerbin - 50 m/s left (!) This is going to be super close and if I lose any efficiency on the Moho landing then the mission's lost, assuming a single stage.

However I think that staging will increase delta-v significantly. Comparing the vacuum delta-v of the fully fueled craft with all the plane parts, and then with none of them:

6642 m/s vs 8619 m/s

Comparing the vacuum delta-v of the craft with a realistic amount of fuel drained in LKO:

5168 vs 6868 m/s

This means that a staged design has a good chance of being able to execute a Moho return mission. TWR at low Moho orbit will be about 1.7 which will be fine for a good landing profile.

[Quincunx]

On 4/5/2021 at 10:54 AM, camacju said:

I realized - there's actually one more destination that needs to be addressed: Moho. And the margins might be really tight. I might actually need to stage some parts off for the required delta-v.

Assume I have 5200m/s in LKO since that's what I had last time, 840-850 m/s to Mun transfer, assume 850 - 4350 m/s left

Kerbin-Eve-Kerbin-Eve-Moho gravity assist chain - 1050 m/s to capture using deep space maneuvers and Moho gravity assists- 3300 m/s left (This might be an overestimate. Last time I did this strategy I encountered Moho's orbit at a bad point in the orbit. Likely this will be better if I encounter Moho at periapsis)

Moho orbital velocity at this point is 1050 m/s, so assume 1150 m/s to land and 1100 m/s to take off

Then 1050 m/s to get back to Eve and then back to Kerbin - 50 m/s left (!) This is going to be super close and if I lose any efficiency on the Moho landing then the mission's lost, assuming a single stage.

However I think that staging will increase delta-v significantly. Comparing the vacuum delta-v of the fully fueled craft with all the plane parts, and then with none of them:

6642 m/s vs 8619 m/s

Comparing the vacuum delta-v of the craft with a realistic amount of fuel drained in LKO:

5168 vs 6868 m/s

This means that a staged design has a good chance of being able to execute a Moho return mission. TWR at low Moho orbit will be about 1.7 which will be fine for a good landing profile.

Do I understand you correctly?

1. LKO - Munar GA - resonant Kerbol orbits: 850 m/s

2. Kerbin - Eve - Kerbin - Eve - Moho capture: 1050 m/s

3. Moho capture - Moho surface: 1150 m/s

4. Moho surface - Moho orbit: 1100 m/s

5. Moho - Eve - Kerbin AC - Kerbin surface: 1050 m/s

Firstly, these dV estimates add up to 5200 m/s, not 5150 m/s. Assuming they're correct, your burn to break Moho orbit would leave you running on fumes.

But the wiki has Moho orbital velocity as 795 m/s, not 1050 m/s, and the dV chart shows that a Moho landing costs ~870 m/s, not 1150 m/s. This frees up 280 m/s on landing and 230 m/s on takeoff.

The margins are still tight, and GAs are definitely necessary, but it should still be doable with your single-stage craft. All told the mission would cost 4700 m/s. And in fact you could save even more with the braking technique from before when landing on Moho.

By my maths, you have enough for this mission with a comfortable margin for error. What do you think?

EDIT: I did some poking around on the forums, and it seems the consensus is that Moho is actually the hardest planet to land on and return from. There also seems to be some disagreement about whether encountering Moho at periapsis or apoapsis is better:

Quote

On 8/12/2013 at 11:00 AM, Mr Shifty said:

For a Hohmann transfer, here are the considerations:

1) For a periapsis rendezvous, your transfer ellipse will be smaller, and so it will take more delta-V to lower your orbit from Kerbin's heliocentric altitude to Moho's.

2) For an apoapsis rendezvous, you're meeting Moho when its speed is slowest, but your orbital speed is highest, so it will take more delta-V to get captured.

Sounds like a Moho landing on one orange tank is more complicated (and difficult) than I thought...

Edited April 7, 2021 by Quincunx

[camacju]

1 hour ago, Quincunx said:

All told the mission would cost 4700 m/s.

I was using figures from some Moho missions I previously did. The 1050 m/s quote is from an elliptical Moho orbit, not low circular orbit, which means that if you use the circular orbit figure, your capture burn will be larger. Maybe I'm overestimating how hard it will be, but a Moho SSTO is pretty hard by itself. I don't know how the additional restriction of having to use one orange tank will play into it.

1 hour ago, Quincunx said:

I did some poking around on the forums, and it seems the consensus is that Moho is actually the hardest planet to land on and return from.

That's not really correct. The only challenge with Moho is getting there in the first place, which is still pretty hard if you don't use gravity assists. However with gravity assists it becomes much easier to manage.

Tylo requires more delta-v to land and return, just because of its high gravity. You need minimum 4200 m/s to land on Tylo and return to orbit, plus another 1600-2000 to capture and escape. That's not even counting the Kerbin->Jool transfer, which is 2000 more m/s if you don't use gravity assists, and 850 if you don't.

Eve is harder than Tylo because of the high gravity and thick atmosphere. You lose a lot of fuel to drag.

Eeloo is also harder to get to with a direct transfer since it's so far away.

2 hours ago, Quincunx said:

There also seems to be some disagreement about whether encountering Moho at periapsis or apoapsis is better:

Since I can use gravity assists, encounter at periapsis is always better.

[Hotel26]

14 minutes ago, camacju said:

2 hours ago, Quincunx said:

There also seems to be some disagreement about whether encountering Moho at periapsis or apoapsis is better:

Since I can use gravity assists, encounter at periapsis is always better.

It's not intuitive (hence the disagreements) but I think it is now clear-cut.  See: https://forum.kerbalspaceprogram.com/index.php?/topic/197273-moho-periapsis-for-return-trip-to-kerbin/&do=findComment&comment=3872499

Borrowing the table from that citation:

"I have been able to determine the orbital speed at Apoapsis and Periapsis of a) Moho and b) an HETV with apoapsis at 13.318 Gm (Kerbin altitude):"

	alt: 3.949 Gm	alt: 6.054 Gm
Moho	18,278.8 m/s	12,185.9 m/s
HETV	20,614.6 m/s	15,917.9 m/s
dV	2,335.8 m/s	3,732.0 m/s

I think the "explanation" is that the two fastest speeds of those orbits "match" better than the fastest and slowest speeds of the orbits, respectively.  (Obviously, since they do.)

In addition, this suggests that if you plan to meet Moho at one of its ecliptic nodes -- without a previous inclination change -- its DN is preferable because it is closer to its PE than its AP.

Mr Shifty (quoted above) is correct in noting that the dV saving in my table above (1.4 km/s) is offset by a higher price in establishing a deeper Kerbolar periapsis, but that's less than 1.4 km/s.

Edited April 7, 2021 by Hotel26

[Quincunx]

10 hours ago, camacju said:

That's not really correct. The only challenge with Moho is getting there in the first place, which is still pretty hard if you don't use gravity assists. However with gravity assists it becomes much easier to manage.

Tylo requires more delta-v to land and return, just because of its high gravity. You need minimum 4200 m/s to land on Tylo and return to orbit, plus another 1600-2000 to capture and escape. That's not even counting the Kerbin->Jool transfer, which is 2000 more m/s if you don't use gravity assists, and 850 if you don't.

Eve is harder than Tylo because of the high gravity and thick atmosphere. You lose a lot of fuel to drag.

Eeloo is also harder to get to with a direct transfer since it's so far away.

Right... Derp... Completely obvious... How could I EVEn say that Moho was harder to land and return from? It's like I don't know anything about this game... my apologies!

I think you captured the gist of my argument in your second sentence. Moho is pretty difficult to get to w/o GAs. But GAs change the whole story. Then the question is whether one orange tank is enough, and I agree a single-stage craft would be more difficult still. It would probably be easier to stage the plane parts off. Still, being able to land horizontally should save you some dV through braking, and taking off horizontally should save you some dV from gravity losses, so maybe attaching the landing gear to the orange tank would be advantageous. Then it can take off from Moho like a wingless plane. You showed that airless horizontal TO from Eeloo is possible, maybe it's still possible with Moho's gravity?

And I agree, if you use GAs to get to your orbit, the only disadvantage of a Moho PE encounter (more fuel to get the encounter) is offset by your dV savings. That makes sense.

I'm a bit busy to try such a mission myself, but I might give it a shot later on. I'm also looking at your numbers for Tylo.

If a fully fueled craft with (without) all the plane parts is 6642 m/s (8619 m/s), then you could stage the plane parts in LKO leaving you 6755 m/s dV. Then:

- 850 m/s for Jool capture with GA: 5900 m/s left

- Minimum 4200 m/s for Tylo landing and orbit: 1700 m/s left

- Minimum 1600 m/s for Jool escape: 100 m/s left (!)

Maybe a return trip to Tylo is barely possible on a single orange tank? I don't know how good the TWR of the RAPIER is, so it might not be suitable for takeoff from Tylo. Sorry for my ignorance!

[camacju]

18 minutes ago, Quincunx said:

Maybe a return trip to Tylo is barely possible on a single orange tank? I don't know how good the TWR of the RAPIER is, so it might not be suitable for takeoff from Tylo. Sorry for my ignorance!

It's definitely impossible without a pretty significant design change. The Rapier's specific impulse is really low and the TWR of the Nerv is too low also. This means that the craft probably won't even be able to handle the Tylo landing - you'll either run out of fuel or not be able to slow down.

As it is a Tylo SSTO requires lots of optimization that just isn't possible with the restriction of having to use only one orange tank.