Early passenger SSTO

[Zamolxes77]

I started new career in 1.8.1, on moderate, I found myself semi reliant on contracts to earn the massive amount of cash needed to upgrade the facilities. One condition I put upon myself, is 100% recoverable craft.

Mun orbit passenger contracts are very lucrative, for 5-6 passengers, so I started a quest to design a SSTO plane that can do that, using my current level of technology - panther engines and mk2 body.

Unfortunately there aren't many SSTO planes with those requirements on the net, to draw inspiration from. After many tweaks, I was able to build one, unfortunately only made it into LKO, with 200 dV left. Here is my design, it uses 4 panthers and 2 reliants:

Please let me know what you think and if you have any advice on how to improve on the design. Is entirely possible I don't have the technology to reach Mun yet, without rapiers.

Edited December 31, 2019 by Zamolxes77

[vyznev]

Hmm. Have you considered a two-stage recoverable design? Like flying the craft to LKO in one piece, then decoupling and having the second stage fly off to the Mun while the first stage re-enters and lands back on Kerbin. It's a bit tricky to design both stages so that they can safely land separately after decoupling, but it's doable.

It's also not strictly necessary for the first stage to actually reach orbit — if you're a few hundred m/s short of orbital velocity with an apoapsis around 80–100 km or so, you can decouple the second stage and have it boost itself to orbit before the first stage re-enters. You can't really land back at KSC that way, though. (Here's an example of the concept, although that one uses higher-tech parts and the second stage isn't designed to land since it's an interplanetary probe.)

It's even possible to fly a Falcon 9 style mission without reloading in KSP by launching the first stage into a sufficiently high suborbital trajectory that the second stage can circularize before the first stage re-enters. With a steep enough ascent trajectory, even return-to-launch-site is possible.

(Ps. Your screenshot doesn't show up for me unless I first visit the link directly. It seems your image host doesn't allow hotlinking. Try e.g. imgur instead.)

[Cavscout74]

6 hours ago, Zamolxes77 said:

using my current level of technology - panther engines and mk2 body

The Mk 2 body is probably the worst possible choice for a low to mid tech spaceplane.   I don't have any other helpful advice - my closest spaceplane design to your requirement is a Panther/NERV 1.25m fuselage with only 2 passengers plus pilot.  And it doesn't have enough dV to even get a Mun fly-by after making orbit - only 300 or so dV once in LKO.  Maybe 400 if I flew extra carefully

[Zamolxes77]

On 12/31/2019 at 10:29 PM, Cavscout74 said:

The Mk 2 body is probably the worst possible choice for a low to mid tech spaceplane. 

Why is that, it used to be pretty good ?

 

On 12/31/2019 at 10:00 PM, vyznev said:

Hmm. Have you considered a two-stage recoverable design?

Yes, in fact that's how I fly all my missions: booster into LKO, land the booster, then 2nd stage goes to do the mission. I know about Falcon 9 style missions, though I haven't tried them yet. Still struggling with new aero model, takes me 3300-3500 dV to get into orbit, while it used to take me 2900-3000.

[herbal space program]

On 12/31/2019 at 5:58 AM, Zamolxes77 said:

I started new career in 1.8.1, on moderate, I found myself semi reliant on contracts to earn the massive amount of cash needed to upgrade the facilities. One condition I put upon myself, is 100% recoverable craft.

Mun orbit passenger contracts are very lucrative, for 5-6 passengers, so I started a quest to design a SSTO plane that can do that, using my current level of technology - panther engines and mk2 body.

Unfortunately there aren't many SSTO planes with those requirements on the net, to draw inspiration from. After many tweaks, I was able to build one, unfortunately only made it into LKO, with 200 dV left. Here is my design, it uses 4 panthers and 2 reliants:

Please let me know what you think and if you have any advice on how to improve on the design. Is entirely possible I don't have the technology to reach Mun yet, without rapiers.

This seems doable to me, but unfortunately your image link appears to be  broken. What rocket engines besides the Reliant do you currently have available? Do you have everything up through the 160 science tier? Since the Panther should easily be able to get you above 20km, I would think the Terrier or Poodle engine would actually be your best bet for the rocket part since they have much better vacuum ISP than the Reliant. I may give this a try later myself...

Edited January 2, 2020 by herbal space program

[Zamolxes77]

It was actually very difficult to achieve, Panther seem to cut off very early, around 14 km or so they burn out. I couldn't get more than 900 or so m/s using them. According to KSP wiki, their multiplier depends on atmospheric pressure, so you want to be very low when you do your speed run, I pushed the engines to 209kN, for an engine that maxes out at 200kN. Beyong Mach 2.6, their power drops rapidly.

Here is the image, I rehost it:

Yeah I have all the engines from 160 science now, Terriers are not powerful enough to take this thing out, is quite heavy, poodle might work, I haven't tried it. Unlocked nuclear last night and as soon as I get more cash, I'll get the whiplash.

Edited January 2, 2020 by Zamolxes77

[herbal space program]

19 minutes ago, Zamolxes77 said:

It was actually very difficult to achieve, Panther seem to cut off very early, around 14 km or so they burn out. I couldn't get more than 900 or so m/s using them. According to KSP wiki, their multiplier depends on atmospheric pressure, so you want to be very low when you do your speed run, I pushed the engines to 209kN, for an engine that maxes out at 200kN. Beyong Mach 2.6, their power drops rapidly.

Here is the image, I rehost it:

 

Yeah I have all the engines from 160 science now, Terriers are not powerful enough to take this thing out, is quite heavy, poodle might work, I haven't tried it. Unlocked nuclear last night and as soon as I get more cash, I'll get the whiplash.

If nukes are allowed then I'm absolutely sure it's possible. One thing I'm noticing about your design is it has very little wing area for its mass, which makes flying up high much harder due to the drag incurred by the high AoA you need. Also, are your wings tilted slightly up relative to your fuselage? That angle of incidence will help you fly witha lower overall AoA and therefore go faster. Wet wings are also really helpful in increasing efficiency, since you get the fuel they hold for free in terms of drag, but I guess you haven't reached that tech level yet. Also I concur with @Cavscout74 that Mk1 is much more drag-efficient than Mk2, so definitely switch to that. I'm not sure if it's allowed in career mode, but you can use f12 to look at your aero characteristics and also alt-F12 to enable displaying part-specific drag in the PAW, which can really help in rooting out drag issues.

Edited January 2, 2020 by herbal space program

[Cavscout74]

5 hours ago, Zamolxes77 said:

Why is that, it used to be pretty good ?

It holds the same quantity of fuel as the 1.25m with substantially higher drag and higher dry mass as well (at least for the 1.25m LF tank [0.25 tons] vs Mk2 short LF tank [0.29 tons], I wasn't about to check the numbers on everything)

[herbal space program]

So I came up with one this evening that makes LKO with around 1,100 m/s. Do you want to see it?

[έķ νίĻĻάίή]

Sorry my dude, but I suck at sstos. You can have a look at my craft on kerbalx for example sstos, but they were all made in sandbox...

I’ll try though.

Edited January 3, 2020 by έķ νίĻĻάίή

[Zamolxes77]

2 hours ago, herbal space program said:

So I came up with one this evening that makes LKO with around 1,100 m/s. Do you want to see it?

Definitely

[herbal space program]

15 hours ago, Zamolxes77 said:

Definitely

Here it is in the SPH. Total mass is 56.8t, vacuum dV of the rocket stages is 2879 m/s. It has two MK1 passenger modules, at the front of the stacks left and right of the cockpit, and I'm pretty sure it doesn't have any parts you haven't unlocked yet. It has 3 Panther and 2 Swivel engines, each with a backwards-facing fairing in front of it to reduce otherwise severe back-end drag. The substantial wings are pitched up a couple of degrees relative to the fuselages, to generate lift even when the fuselages have an AoA of zero. I also have 5 intakes for 3 engines, which is a good idea if you're going to go as high as you can on them. Since you presumably don't have the Z-1000 battery yet, I put a couple of draggy z-400 ones in the service bay in the center stack. If I were building this in Sandbox, I'd have definitely used wet wings to lower overall drag even more, but I'm assuming you don't have those yet.

In terms of flight profile, I started off at a low rate of climb and built speed low in the atmosphere, in dry mode. With this plane, I was never quite able to break the sound barrier in dry mode, but I could get very close to Mach 1. Turning on the afterburners would then push it across fairly quickly, after which I could then switch back to dry mode and only slowly lose velocity while climbing further at about 10 degrees of pitch.

Although I never really got above Mach 2.5, I found that I was able to maintain that speed almost all the way to 20 km on the Panthers alone. I would start to lose speed at around 18.5 km, at which point I would pitch up to 20 degrees and fire up the Swivels. The Panthers would typically flame out at ~23 km, and the rest of the ride to orbit was pretty straightforward:

 

 

I always ended up with quite a bit of extra LF in the tank as well, so there is plenty left to land under power. Rather too much in fact, which represents a point of potential improvement. And although I think you have plenty of dV to orbit the Mun with this craft, I'm sure it would tolerate a couple more small tanks to add another 100-200 m/s. I'm pretty sure you could land it on Minmus then as well!

Edited January 4, 2020 by herbal space program

[Zamolxes77]

Very nice, thank you for the post. That should point me in the right direction.

I have several questions:

1. Are you sure you don't mix up the modes ? Dry mode is when Panthers have cowlings closed, 300 m/s max, wet mode is when plumes are red and you go considerably faster, 2.6 Mach.

2 hours ago, herbal space program said:

In terms of flight profile, I started off at a low rate of climb and built speed low in the atmosphere, in wet mode. With this plane, I was never quite able to break the sound barrier in wet mode, but I could get very close to Mach 1. 

2. Why so many wings ? Did lift was severely reduced in 1.8 ? Or they provide high drag in upper atmosphere for quick deceleration, to avoid overheating (I used to do that)?

3. Why Swivels ? Only for gimbal ? They weight more and they're less efficient than Reliant, both is ASL and VAC. Will some extra torque make up for the gimbal ? I have to test that.

4. Fairings around the engines ? Wow drag is really a pain it seems in 1.8. Nice idea, I observed that certain engines seem to have a lot of drag. Yesterday I figured out how to investigate drag, wish there was a mode that would float numbers over selected parts with the drag. Offsetting the engines inside the tanks don't eliminate that drag ?

Again, thanks for sharing !

[herbal space program]

5 hours ago, Zamolxes77 said:

Very nice, thank you for the post. That should point me in the right direction.

I have several questions:

1. Are you sure you don't mix up the modes ? Dry mode is when Panthers have cowlings closed, 300 m/s max, wet mode is when plumes are red and you go considerably faster, 2.6 Mach.

2. Why so many wings ? Did lift was severely reduced in 1.8 ? Or they provide high drag in upper atmosphere for quick deceleration, to avoid overheating (I used to do that)?

3. Why Swivels ? Only for gimbal ? They weight more and they're less efficient than Reliant, both is ASL and VAC. Will some extra torque make up for the gimbal ? I have to test that.

4. Fairings around the engines ? Wow drag is really a pain it seems in 1.8. Nice idea, I observed that certain engines seem to have a lot of drag. Yesterday I figured out how to investigate drag, wish there was a mode that would float numbers over selected parts with the drag. Offsetting the engines inside the tanks don't eliminate that drag ?

Again, thanks for sharing !

1. Yes, you are right. I actually meant dry mode when I said "wet mode". 

2. Because the weight and drag of all the wings is offset by the extra lift that allows you fly near your prograde vector, especially up high where the air is thin. Having a really high AoA with all your fuselages will just kill you with drag that does not produce any lift. Hence the pitched-up placement of the wings also, to allow them to have a positive AoA while all the fuselages are pointed prograde.  I have built planes that way since at least 1.2 or so. Just keep adding wings to your own design and see what happens!

3. A fair point, although Swivels actually have a slightly better vacuum  ISP than Reliants (320 v. 310).  This small difference  may be mostly offset by the  added weight, but the gimbals do come in handy so long as you have enough TWR.  Could go either way for what I have, but for anything larger, I agree the better TWR of the Reliants will become critical. In fact, I noted tardily that I only had room for 4 passengers when 5-6 were required, so I may try them on a version with an extra crew cabin.

4. Drag is always a key consideration whenever you  are trying to fly something into LKO at a low TWR. The fairings only weigh like 0.2 tons and reduce the overall drag of the engines by more than half, so they are often worth it. The Swivels in particular had awful drag, so I covered them first, but then I saw better performance when I covered the Panthers also. As to clipping stuff, I think that will only cheat the drag model if you then put all the clipped-together parts inside a fairing. Not really Cricket in my book, but YMMV. Anyway, I look forward to seeing what you come up with!

...As an update, When I switched to the Reliants I was indeed able to get better overall performance, getting roughly the same dV on orbit as before, despite an added passenger module for a total capacity of 6. The gimbals were definitely missed though!

Edited January 4, 2020 by herbal space program

[TheFlyingKerman]

On 1/3/2020 at 3:07 AM, Zamolxes77 said:

Yes, in fact that's how I fly all my missions: booster into LKO, land the booster, then 2nd stage goes to do the mission.

I am not sure if an ssto spaceplane is really cheaper than that.

[Laie]

Me as I see the topic: I've got just the thing for you!
After reading the post: or maybe not.

Still, from the thinking outside the box department, here's a very early passenger plane:

Not strictly SSTO, but I'd like to remind you that boosters are dead cheap. Decouplers aren't, but since they've been made hollow rings they can be used in the above fashion. Less than 1000 funds thrown away... If I tried to make it SSTO it would be much bigger and more expensive and I'm not entirely sure it would actually save money.

Of course, the above is LKO only.

On 12/31/2019 at 2:58 PM, Zamolxes77 said:

Mun orbit passenger contracts are very lucrative, for 5-6 passengers, so I started a quest to design a SSTO plane that can do that,

Don't bother. Not at your techlevel, and probably not at all. If you must use a plane, take it no further than LKO. All the wings and jets are only dead mass on the way to the Mun, requiring you to bring more propellant. And more wings and jets to carry that propellant, and so on.

While later engines make it possible, it's still an execise in over-engineering. Do it if you like, but don't pretend it's efficient.

The proper way to do it is to have a shuttle to LKO, and then another vessel to take it from there. Use a Mk3 plane that carries a spacecraft in the cargo bay, for example.

ETA: like this:

55t roll out on the runway, 30t arrive in orbit, but only 8t got to the Mun. Craft file.

Edited January 4, 2020 by Laie

[herbal space program]

10 hours ago, TheFlyingKerman said:

I am not sure if an ssto spaceplane is really cheaper than that.

Well those Panther engines can get you to Mach 2.5 and almost 20 km on 10 times less propellant than any other solution available at that tech level, so even if I were to use a more conventional rocket with a recoverable booster, I'd consider making the booster out of those. As to the overall cost of the SSTO, the one I made above is ~53,000 to build and ships ~3,500 worth of fuel, which would represent the total non-recoverable mission cost. Of that, only ~860 is required to do the Munar orbit leg from LKO with 6 passengers, which is less than even the most trivial early contracts pay in hard career mode.  There is also the matter of the easy complete recovery of non-fuel costs that the ability to fly your plane right back to the runway affords you. Even a recoverable booster is generally going to get recovered somewhere downrange, which will incur a significant penalty. And splashing down any separate Munar excursion module will similarly require a tedious level of precision aerobraking to get you splashed down right next to the KSC. Either that or you have to do even more precise aerobraking and/or burn a whole bunch of propellant to re-rendezvous with the shuttle on LKO. Of course in principle what @Laie said about a shuttle system being the most cost-effective way is true, but unless cost efficiency is the single most important objective, you have to weigh that fact against the ease and convenience of taking the whole show off from the runway and landing it there again. 

Edited January 4, 2020 by herbal space program

[Laie]

3 minutes ago, herbal space program said:

but unless cost efficiency is the single most important objective, you have to weigh that fact against the ease and convenience of taking the whole show off from the runway and landing it there again.

Well, if convenience comes into play... putting a cheap rocket on the launchpad and landing it wherever you end up isn't all that costly, either. I slapped together a quick mock-up that costs <20k to roll out. @Zamolxes77 How does that compare to the payout, by the way?

15 minutes ago, herbal space program said:

And splashing down any separate Munar excursion module will similarly require a tedious level of precision to get you splashed down right next to the KSC.

The munar vessel only costs 5k dry and was a little cheaper to launch. So there is some leeway for the splashdown: almost to the Great Desert. If you manage to come down any closer to KSC, you've saved money.

But in the end, it's the convenience argument all over again: compared to the payout from the mission, the cost of landing a hundred kilometers closer or further from KSC comes out as a rounding error. Which won't help you if you insist on getting it just right.

[Zamolxes77]

I'm not doing it to be efficient. If you want efficiency, rockets is the way to go. 

I'm simply sick of launching every mission, then having to fly the booster back every time. Also I'm looking for variety, something different, achieving something in fewer launches but in a different way. I also like a challenge, see what's possible to design using early tech. Internet is filled with SSTO's on which you slap rapiers on then call it good.

Your out of the box idea seems interesting, basically an almost chemical SSTO, it might worth investigating.

4 hours ago, Laie said:

Well, if convenience comes into play... putting a cheap rocket on the launchpad and landing it wherever you end up isn't all that costly, either. I slapped together a quick mock-up that costs <20k to roll out. @Zamolxes77 How does that compare to the payout, by the way?

Well I'm at the point where a 25 ton (payload) booster isn't exactly cheap at around 40k. And most contracts for such missions pay around 100k. If I were to discard that, that would make the payout not really worth it. I'm going for a 100% recoverable career. A 20k booster won't cut it.

[sturmhauke]

On 12/31/2019 at 12:29 PM, Cavscout74 said:

The Mk 2 body is probably the worst possible choice for a low to mid tech spaceplane.

On 1/2/2020 at 2:03 PM, herbal space program said:

Also I concur with @Cavscout74 that Mk1 is much more drag-efficient than Mk2, so definitely switch to that. 

On 1/2/2020 at 5:05 PM, Cavscout74 said:

It holds the same quantity of fuel as the 1.25m with substantially higher drag and higher dry mass as well (at least for the 1.25m LF tank [0.25 tons] vs Mk2 short LF tank [0.29 tons], I wasn't about to check the numbers on everything)

Mk2 does have a couple advantages over Mk1:

1.  Heat tolerance. Mk1 spaceplanes are far more likely to melt on reentry.
2. Cargo bays. Your only cargo options for Mk1 are fairings and service bays, which aren't as easy to use.

[herbal space program]

3 hours ago, sturmhauke said:

Mk2 does have a couple advantages over Mk1:

1.  Heat tolerance. Mk1 spaceplanes are far more likely to melt on reentry.
2. Cargo bays. Your only cargo options for Mk1 are fairings and service bays, which aren't as easy to use.

It also looks a whole lot nicer, lets you ship an engineer in your cockpit, and has inline docking ports. But if you're trying to squeeze every last bit of performance out of a low-TWR situation, Mk1 just lets you go higher and faster pretty much every time. Mk3 can be better still, because more mass/surface area, but OP does not have that yet.

On 1/4/2020 at 5:10 PM, Zamolxes77 said:

I'm not doing it to be efficient. If you want efficiency, rockets is the way to go. 

Actually, I think the space plane with a detachable/bay-enclosed Munar excursion module that @Laie posted is the most cost-efficient solution. Those Panther engines really do get you going pretty fast and pretty high for next to no fuel, and if you ditch the whole plane and just orbit the Mun with a minimal module, you are basically doing that as cheaply as it can possibly be done from LKO. You just have to land the two components separately with that solution, which increases the grind factor. Given that we're talking maybe a few hundred more to fly the whole plane there, in terms of player time/effort I think the one-craft space plane solution is by far the most efficient.

Edited January 6, 2020 by herbal space program

[TheFlyingKerman]

Elaborating on @Laie's idea, I built a Munar crew module riding on my reusable lifter (the SRB's land back to the KSC area after staging).

The crew module sits 8, and has 1750 Dv. It is light and heat resistant so that 2-3 pass of aerobreaking is enough to bring it down from Munar transfer orbit to LKO. Both the lifter and crew can glide back to KSC for nearly full refund. The total fuel cost per launch is about 3800 funds, not much more than the space planes above.

[SiWalder]

Hi mate,

I like your original design, it would be a shame not to put it to use

You're probably aware of this already, but you'll find that once you've done a couple of tourism contracts, they start getting more adventurous and wanting much more that just mun or minums orbits to satisfy the contract,  That's always been my experience at least.

If you can squeeze a little more DV out of your original design it'll work really well as an LKO rescue craft which are always good quick, money earners.  LKO rescue missions seem to persist throughout a career mode as well.

I know whenever you try to squeeze Dv out of an SSTO design, you seem to end in a pit of diminishing returns, but... have you considered reducing the number of engines by 1.  I'd be tempted to swap the bi coupler at the back for a single MK2 to 1.25 adapter and try 4 jets and one rocket engine, and if that leaves the rocket stage too weedy a 3 jet, 2 rocket version, although the Dv saving from the later  probably won't be great.

I'm sure I've got a 3 crew panther/reliant plane that gets to LKO with about 800 Dv left.  I'll try and dig it out when I get home,. although it's a MK1 and doesn't look as good as yours.

Si

 

[SiWalder]

I managed to add 2 more 400 LF&OX tanks behind the inner air intakes to your original design for a bit more Dv. It still makes orbit without a struggle.