Is Oxidizer required for SSTO ascent from Laythe?

[Firemetal]

So I'm designing an SSTO to go to Laythe and back. I have one which is around 100-200m and I really don't know whether it has the DV required. It has four rapiers, two whiplashes and 2 nukes. Good efficiency comes with a price. With the Nukes only, it has .15 TWR. I had to use all the oxidizer for circularization purposes (Inside the atmosphere too )  and I managed to get into a 95x95 orbit around Kerbin. Had to circumnavigate just inside the atmosphere to my 95km orbit. But I have no oxidizer. Now I'm guessing with such a low TWR, I'd probably need oxidizer however once there, I will have lost a lot of fuel and that will raise my TWR. I also know that Laythe has a 50km high atmosphere. So can I do it without oxidizer?

Edited July 20, 2016 by Firemetal
Ascent "to" Laythe? FROM you mean.

[Snark]

Taking off from Laythe is a very similar experience to taking off from Kerbin.  The atmosphere is a little bit thinner... but the gravity's a little bit lighter, too, and it tends to cancel out.  So the challenge of building a LF-only SSTO for Laythe is pretty close to the challenge of doing it on Kerbin.

I know that there are people who have built SSTO's that can get to Kerbin orbit with LF only, using nothing more than air-breathers and nukes.  I'm not one of those people ... not really an SSTO guy myself.  But I know there are people who've done it, so if it's possible on Kerbin, it's possible on Laythe, too.

For myself:  on those occasions when I do fly an SSTO that uses Rapier + LV-N, I typically include a little bit of oxidizer to give it a brief high-TWR boost after the Rapier's air-breathing thrust conks out.  I mean, why not?  I've got the Rapiers sitting there anyway, and a little bit of oxidizer can really help bridge the gap, in my experience.  It helps to give that extra bit of "breathing space" (no pun intended) so that the LV-N will have more time to work and get the Pe out of atmosphere before falling back in.

[Firemetal]

10 minutes ago, Snark said:

Taking off from Laythe is a very similar experience to taking off from Kerbin.  The atmosphere is a little bit thinner... but the gravity's a little bit lighter, too, and it tends to cancel out.  So the challenge of building a LF-only SSTO for Laythe is pretty close to the challenge of doing it on Kerbin.

I know that there are people who have built SSTO's that can get to Kerbin orbit with LF only, using nothing more than air-breathers and nukes.  I'm not one of those people ... not really an SSTO guy myself.  But I know there are people who've done it, so if it's possible on Kerbin, it's possible on Laythe, too.

For myself:  on those occasions when I do fly an SSTO that uses Rapier + LV-N, I typically include a little bit of oxidizer to give it a brief high-TWR boost after the Rapier's air-breathing thrust conks out.  I mean, why not?  I've got the Rapiers sitting there anyway, and a little bit of oxidizer can really help bridge the gap, in my experience.  It helps to give that extra bit of "breathing space" (no pun intended) so that the LV-N will have more time to work and get the Pe out of atmosphere before falling back in.

So how much oxidizer do you suggest to be left?

[bewing]

Well, I'm in the opposite boat from Snark. I've built a lot of LF-only SSTO spaceplanes, but I've never been to Laythe. But with one refueling stop at the Mun, and maybe another out around Jool someplace, it should be doable. My spaceplanes tend to be under 30 tonnes, however. It sounds like yours is a monster, and that makes everything a lot harder.

[Firemetal]

Well it is a pretty short SSTO as Mk3 SSTOs go. If you want I can upload a pic. 

[Aegolius13]

I recently did a Laythe SSTO with 2 nukes and 2 rapiers.  Was able to get to orbit from Laythe pretty really without using any oxidizer, which I don't think would have been possible on Kerbin.  The thicker atmosphere up top on Laythe, though difficult for aerobraking, seemed to help the rapiers get closer to escape on their own.    I had pretty similar amounts of fuel on board in both cases.

But my plane was pretty small (Mk 2) and passenger only.  If your nukes provide lousy TWR, stands to reason they may need some help.

One other note: takeoff from Laythe can be trickier due to thinner surface air and lack of a smooth runway.  I had to briefly turn on my nukes to make sure I did not re-touch right after takeoff.

[Firemetal]

5 minutes ago, Aegolius13 said:

I recently did a Laythe SSTO with 2 nukes and 2 rapiers.  Was able to get to orbit from Laythe pretty really without using any oxidizer, which I don't think would have been possible on Kerbin.  The thicker atmosphere up top on Laythe, though difficult for aerobraking, seemed to help the rapiers get closer to escape on their own.    I had pretty similar amounts of fuel on board in both cases.

But my plane was pretty small (Mk 2) and passenger only.  If your nukes provide lousy TWR, stands to reason they may need some help.

One other note: takeoff from Laythe can be trickier due to thinner surface air and lack of a smooth runway.  I had to briefly turn on my nukes to make sure I did not re-touch right after takeoff.

Thanks! Could you post a pic of your SSTO? That would be great! Thanks!

[Aegolius13]

Sure, I posted a pic along with a question at:

 

It was probably not the most efficient plane ever (doubt it could get from Kerbin to Laythe and back on one tank without some very fancy flying), but it generally got the job done. 

I should also note that, after posing that, I changed the intakes to shock cones and added some angle of incidence on the wings to cut drag while climbing.  Performance seemed to get a fair amount better.

[Firemetal]

Woah. That thing got to Laythe and back???? My mind is blown. Maybe I should think smaller.

Edit: Wait you used refueling right?

Edited July 20, 2016 by Firemetal

[Aegolius13]

I took off from Kerbin about half full on fuel, then topped off at my station in LKO.  Used a gravity assist at Tylo to capture around Jool and intercept Laythe, did ~500m/s retro burn at Laythe to get to safe aerobrake speed, aerobraked the rest of the way to low orbit, landed, and got back to orbit.  I had about 1100 delta-v left at that point, which would theoretically get back to Kerbin intercept, but not capture without  a Mun gravity assist or Kerbin aerobrake (if that's possible).  With more careful maneuvering along the way I might have been able to save a few hundred more delta-v. 

I think there's an old SSTO to Laythe challenge on these boards where some folks did it without refueling, but those planes generally have very little payload.  

 

[Firemetal]

22 minutes ago, Aegolius13 said:

I took off from Kerbin about half full on fuel, then topped off at my station in LKO.  Used a gravity assist at Tylo to capture around Jool and intercept Laythe, did ~500m/s retro burn at Laythe to get to safe aerobrake speed, aerobraked the rest of the way to low orbit, landed, and got back to orbit.  I had about 1100 delta-v left at that point, which would theoretically get back to Kerbin intercept, but not capture without  a Mun gravity assist or Kerbin aerobrake (if that's possible).  With more careful maneuvering along the way I might have been able to save a few hundred more delta-v. 

I think there's an old SSTO to Laythe challenge on these boards where some folks did it without refueling, but those planes generally have very little payload.  

 

Ok this is an awesome idea. I originally wanted to do it without refueling but lets face it: that is hard as heck and I haven't even gone to Laythe with a rocket yet! I think I'll just launch a similar SSTO to the on you built to LKO and send up a refueling vessel to refuel it. Thanks man! That helped a lot.

[max_creative]

With the LV-Ns, it depends on the size. It sounds rather big for an ssto. If it's irsu, then you don't have a problem. Nukes are HORRIBLE in an atmosphere.

I'm really bad with sstos, but maybe try going really fast really low, then slowly pull up? Then you get good efficiency in the lower atmosphere with the jets, and then the nukes have less work to do in the atmosphere? Again, I'm terrible with planes. 

What I want to know is if a rocket engine only Laythe ssto is a good idea. I don't want to drag a plane to Laythe for my Jool 5 mission.

[Aegolius13]

Yeah, I too wrestled with whether it's "really SSTO" if you refueled, but decided it was consistent with my head-canon that the KSP would make use of orbital infrastructure on such a mission.  And I just didn't think it would be feasible to do the mission with the kind of plane I wanted without it.  I would really like to be able to get back to Kerbin without a second refuel in Laythe orbit (sending a dedicated fuel pod to Laythe on a rocket seems more sketchy to me), but time will tell if I can optimize my design and flying to do so.  

Anyhow, it was quite a fun mission - maybe my favorite in the game so far.  Frustrating at times (blew up trying to aerobrake at Laythe SO many times), but I fine-tuned my skills quite a bit along the way, and it was quite exhilarating when I finally touched down on Laythe in one piece.  Good luck!

 

[Firemetal]

20 minutes ago, Aegolius13 said:

Yeah, I too wrestled with whether it's "really SSTO" if you refueled, but decided it was consistent with my head-canon that the KSP would make use of orbital infrastructure on such a mission.  And I just didn't think it would be feasible to do the mission with the kind of plane I wanted without it.  I would really like to be able to get back to Kerbin without a second refuel in Laythe orbit (sending a dedicated fuel pod to Laythe on a rocket seems more sketchy to me), but time will tell if I can optimize my design and flying to do so.  

Anyhow, it was quite a fun mission - maybe my favorite in the game so far.  Frustrating at times (blew up trying to aerobrake at Laythe SO many times), but I fine-tuned my skills quite a bit along the way, and it was quite exhilarating when I finally touched down on Laythe in one piece.  Good luck!

 

Thanks mate! Yeah when I landed my Duna SSTO about a week ago, (it took me countless tries since Duna's atmosphere is so thin) I was exhilarating inside but outside I was like: "yeah. I landed. Awesome." This was due to one, I was exhausted and two, I was worried that I wouldn't be able to get back but in the end I had a lot of DV to spare.

This helped a lot! Thanks again.  

Edited July 20, 2016 by Firemetal

[Aegolius13]

1 minute ago, max_creative said:

Nukes are HORRIBLE in an atmosphere.

Definitely true at Kerbin, though they get into acceptable ISP surprisingly fast as you climb.  I usually turn mine on around 20km altitude, and they're well above 700 ISP at that point.  If memory serves, at Laythe sea level they were something like 300 ISP, and again improved from there with a climb.  So not great, but probably better than turning the Rapiers onto rocket mode.  As long as the nukes were somewhat competitive with chemical rockets, I thought it best to use them and keep milking the relatively-great ISP from the jet-mode Rapiers. 

 

8 minutes ago, max_creative said:

What I want to know is if a rocket engine only Laythe ssto is a good idea. I don't want to drag a plane to Laythe for my Jool 5 mission.

By "plane," do you mean jets, wings or both?  Not too sure, but unless you're planning on using the same lander to hit Laythe plus the Vall / Tylo, I have to think plane comes out ahead for Laythe.  Rapiers aren't SO inferior as rocket engines than Darts, etc., that I'd pass up the opportunity for 3200 ISP jet mode when you can get it.  

 

 

[Van Disaster]

Long ago I got close enough to Laythe atmosphere escape on jets that I just did the rest on RCS - I think my PE dipped 500m into the atmosphere. It took three hours though, I think, so not exactly practical... ( also jets functioned somewhat higher back then ).

Laythe orbital velocity is somewhat lower than Kerbin, so it is rather easier ( ie, no you don't need ox. If you bring enough you don't on Kerbin either, but that is painful ).

[Firemetal]

1 hour ago, max_creative said:

With the LV-Ns, it depends on the size. It sounds rather big for an ssto. If it's irsu, then you don't have a problem. Nukes are HORRIBLE in an atmosphere.

I'm really bad with sstos, but maybe try going really fast really low, then slowly pull up? Then you get good efficiency in the lower atmosphere with the jets, and then the nukes have less work to do in the atmosphere? Again, I'm terrible with planes. 

What I want to know is if a rocket engine only Laythe ssto is a good idea. I don't want to drag a plane to Laythe for my Jool 5 mission.

Nukes are my favourite engines in the game. So obviously I know they ain't good in the atmosphere. However I was wondering if because the atmosphere height is so low, the rapiers can push the Ap out of the atmosphere on their own without closed cycle.

[Aegolius13]

Whether your apo gets out into vacuum on jet power alone is likely to depend a lot your angle of ascent.  I think you can even do this on Kerbin with a very steep climb... but you'll have a very up-and-down trajectory that requires a lot of delta-v to circularize (like launching a rocket without a gravity turn).  

To get the most efficient takeoff, I think it's better to climb more gradually, and light off your nukes while still in high atmo -- the atmo should be thin enough that the nukes' ISP is reasonable.  Which should be doable on Laythe.  

[Firemetal]

2 hours ago, Van Disaster said:

Long ago I got close enough to Laythe atmosphere escape on jets that I just did the rest on RCS - I think my PE dipped 500m into the atmosphere. It took three hours though, I think, so not exactly practical... ( also jets functioned somewhat higher back then ).

Laythe orbital velocity is somewhat lower than Kerbin, so it is rather easier ( ie, no you don't need ox. If you bring enough you don't on Kerbin either, but that is painful ).

That helps a lot thanks!

 

1 hour ago, Aegolius13 said:

Whether your apo gets out into vacuum on jet power alone is likely to depend a lot your angle of ascent.  I think you can even do this on Kerbin with a very steep climb... but you'll have a very up-and-down trajectory that requires a lot of delta-v to circularize (like launching a rocket without a gravity turn).  

To get the most efficient takeoff, I think it's better to climb more gradually, and light off your nukes while still in high atmo -- the atmo should be thin enough that the nukes' ISP is reasonable.  Which should be doable on Laythe.  

Yup.

 

[KerikBalm]

Its much easier to build a LF only laythe SSTO because:

1) orbital velocity is about 500 m/s lower than kerbin (around 1850 IIRC), which means if you get to 1400 m/s your nukes only need to supply another 450 m/s on laythe as opposed to another 950 m/s on Kerbin

2) the atmosphere is actually thicker at high altitude - your rapiers will produce more thrust high up, and you'll get higher - yet the atmosphere ends lower. Thus the part of the atmosphere that isn't useable for airbreathing and just slows you down is much less.

(doesn't show the much steeper dropoff after 40km)

3) The gravity is only 0.8, this all TWRs are 1.25x higher (except static airbreathing thrust, which is a bit lower due to the thinner sea level laythe atmosphere)

 

LF only should be no problem.

[Champ]

i know many have done a single-stage-to-laythe-and-back-without-refueling, but i wonder : is it possible with life support (ideally, tac ls) ? No payload (just a kerbonaut)

[Firemetal]

5 hours ago, KerikBalm said:

Its much easier to build a LF only laythe SSTO because:

1) orbital velocity is about 500 m/s lower than kerbin (around 1850 IIRC), which means if you get to 1400 m/s your nukes only need to supply another 450 m/s on laythe as opposed to another 950 m/s on Kerbin

2) the atmosphere is actually thicker at high altitude - your rapiers will produce more thrust high up, and you'll get higher - yet the atmosphere ends lower. Thus the part of the atmosphere that isn't useable for airbreathing and just slows you down is much less.

 

(doesn't show the much steeper dropoff after 40km)

3) The gravity is only 0.8, this all TWRs are 1.25x higher (except static airbreathing thrust, which is a bit lower due to the thinner sea level laythe atmosphere)

 

LF only should be no problem.

Thanks! This helped a lot!

 

[KerikBalm]

20 hours ago, Firemetal said:

Nukes are my favourite engines in the game. So obviously I know they ain't good in the atmosphere. However I was wondering if because the atmosphere height is so low, the rapiers can push the Ap out of the atmosphere on their own without closed cycle.

you most certainly can, and you don't even need a particularly steep climb to do it, due to the lower absolute limit for the atmosphere, the higher cutoff altitude for the rapiers, and the lower gravity. The challenge whether or kerbin or laythe, is getting close to orbital velocity before apoapsis, not getting the apoapsis out of the atmosphere before airbreathing cutoff.

The lower gravity gives you about 25% more time before apoapsis for the same speed and angle relative to kerbin, while the lower orbital velocity means you only need to generate <50% of the dV before apoapsis.

To a small extent, drag is less because your AoA can be lower because you don't need to generate as much lift because there is less gravity... but this is minor

[Firemetal]

1 hour ago, KerikBalm said:

you most certainly can, and you don't even need a particularly steep climb to do it, due to the lower absolute limit for the atmosphere, the higher cutoff altitude for the rapiers, and the lower gravity. The challenge whether or kerbin or laythe, is getting close to orbital velocity before apoapsis, not getting the apoapsis out of the atmosphere before airbreathing cutoff.

The lower gravity gives you about 25% more time before apoapsis for the same speed and angle relative to kerbin, while the lower orbital velocity means you only need to generate <50% of the dV before apoapsis.

To a small extent, drag is less because your AoA can be lower because you don't need to generate as much lift because there is less gravity... but this is minor

Ok thanks man! If you're interested here is my Mission to Laythe Mission report!

 

Edited July 21, 2016 by Firemetal
Missino?!