Minmus micro SSTO [STOCK] !

[Zamolxes77]

"KSC has run out of funds ! We're sorry Jeb, Valentina, you have an upcoming mission to Minmus but we cannot afford to give you a capsule. Or parachutes. Or air pressure. Nor snacks!

I'm not going anywhere without snacks, says Jeb.

Well, we can give you two extra seats, think hard whom you want to take with you ... they might become ... your snacks.

Ewwww says Valentina.

On the upside, you get a big radioisotope generator, in the middle of your ... service bay ... for ... heating, yes, HEATING ! Its surrounded by some additional fuel tanks that should shield you from radiation.

Someone saw too many Earther movies, Valentina frowns."

Saw another youtube video with someone taking a small SSTO all way to Minmus, land and come all way back to KSC. I wondered if something similar was possible in current version, 1.1.2, and after about 4 hours of design, YES, it is possible.As one can imagine, on such a SSTO, mass, ANY mass, is at a premium, even 50kg for a control seat, gives significant fluctuations in TWR and alters ascent profile, A LOT. So I had to ruthlesly discard a pressurized cabin, placing 4 seats inside a service bay. For a while I considered even tossing the service bay and just use struts, but that seemed a bit too extreme heheh.

Sadly, I couldn't find a solution that involves vanilla game, at least not yet. Both ends of the spaceplane have to be aerodynamic, sadly there is no stock part that I know of that contains liquid fuel only (for the atomic engine and atmospheric phase) and using available tanks means employing a structural part to resolve the aerodynamics. ANY extra mass is a killer. I would greatly appreciate any suggestions here, as it stands, I end up using Fuel Switch mod that comes with Interstellar, it allows to switch fuel configurations for all stock parts.

A second compromise I had to do is clipping the engines inside each other, and inside the tanks. I don't like this kind of ... exploiting ... three times the mass occupying the same space, oh well, I had to do it, only other solution would have been to employ more structural parts, that have mass and well you know the rest.

Here's the plane in circular LKO, I left KerEngineer windows up. As you can see it has nearly 2100 delta-v left, which is more than enough to get to Minmus, land, take off, come back and land.

 

 It flies very well, I like my planes to be stable and maneuverable, even a rookie shouldn't have any problems taking this into orbit. Is a bit twitchy on the runway at low speeds, probably because the rear landing gear is relatively narrow, but around 30 m/s it stabilizes and takes off around 70-80 m/s. Ascent profile is rather easy: adopt an AoA (angle of attack) that maintains a positive rise in velocity, but without going supersonic bellow 7,000 meters (30 degrees at 0m, 20 degrees at 2000m, 10 degrees at 5,000m). Once at 7 km and around 350 m/s you can start the "speed run" - maintaining 10 - 20 degrees AoA, after 20 km 5 degree AoA. By the time intake air is out, you should be around 24 km up and 1200-1300 m/s.

From there, switch modes on Rapier, raise AP to 75 km then coast to AP and circularize. If everything has been done efficiently, you should run out of oxidizer during circularization phase, finish it with the Nerv.

Here's the plane on factory floor for some detail:

The batteries aren't entirely necessary since power is provided by the radioisotope in the middle, their weight is so small however. I think a 3rd oscar fuel tank can be added next to the other 2 and that should give enough oxidizer to finish circularize with the Rapier, however the ascent phase will become more difficult, lower TWR. Personally I like smooth ascents, but en experienced player could take the plane up with a TWR of .65. At TWR .64 I found this plane un-flyable, it tanks in speed around 350 and while it is recoverable, by diving, you basically waste fuel which will cut into your remaining delta-v once in orbit.

Let me know what you think about it !

Edited July 3, 2016 by Zamolxes77

[Zamolxes77]

- update -

I'm such a retard. Who says I have to use the 2.5m service bay ? Can't a kerbal fit somewhere else? OFF COURSE it does !

It dawn on me, while taking a dump, best ideas come when sitting on the crapper

So IT IS possible to have a Minmus SSTO, round trip, with 100% stock parts, 100% vanilla game, no mods ! It even looks cooler.

 

Note: if you find this too hard to fly, not from maneuvering point of view, but as ascent profile, mk2 drone core can be switched out for a RC-001s guidance unit plus a inline reaction wheel - gain 100 kg there so TWR goes up to .67. The little fuel tank in the front, that was the fuel I had in 2 Oscar tanks before, it can be removed, or more fuel can be added, either as toroidal tanks or oscar ones, fitted in the cargobay. Play around with mass of the plane, watch the TWR and see what you like. P.S. KerEngineer has problems seeing the clipped engine, so it displays the S0 as having no thrust, but once you take off, it recovers. Sadly I couldn't figure out a way to solve the 2 engines occupying same space problem.

- update again -

It turns out kerbals have ... mass. Who knew ! My previous 100% stock model has been tested, empty ... As soon as I added 4 kerbals, ascent profile got shot to hell. 4 kerbals at 93 kg a pop, is a whopping .27 tons. I managed to get into orbit, but only with 1900 delta-v remaining, BEFORE circularize. So it seems I have to eliminate the mk2 drone core, go for the lighter option, also one chair and a kerbal, perhaps even TWO.

[Majorjim!]

Nice work!

 If you place a part small nosecone on the rear of the rapier it will reduce the drag and give you even more dv! Open nodes cause a lot of drag.

 You should fly a full mission to Minmus and take pics!

[Zamolxes77]

Ok, another update. Slightly modified the design, holds only 2 kerbals now and more fuel+oxidizer. Did 4 "simulations" to orbit, 3 out of 4 I managed to arrive with over 1800 delta-v remaining and an ascending node with Minmus of aprox. 1 degree. Its a bit too low for a landing on Minmus mission: 950 m/s to get there, 200m/s to circ, 200 m/s to land, 150m/s to take off, 100m/s to circ, 50m/s to escape, another 100 m/s to lower Kerbin PE, that's all the delta-v budget, no mistakes insurance and no landing fuel, well not much is needed since aerobraking.

Thanks for suggestion with the cone Majorjim, only reason I didn't use its because I need that node to hold a crew cabin for transfer into chairs. Yes I can use a rover to bring them to the plane on runway, but that will be done when testing is complete.

[Majorjim!]

Just now, Zamolxes77 said:

I need that node

You should use Editor extensions man! It allows you to surface attach decouplers.

[Zamolxes77]

Are those editor extensions a mod? NVM, I'll look it up. Here's the pics with "Expedition Minmus"

In orbit, ready for burn :

 

Circularization planning at Minmus:

Landing:

Success ! :

Going home, retrograde orbit:

Last orbit before diving for landing:

Unfortunately, while trying to land, I discovered a critical design flaw: when bingo fuel, CoL is far forward in regard to CoM, the plane twists and banks uncontrollably, until it crashes, its impossible to recover. Don't know how the hell I forgot that step, its pretty much standard procedure when designing SSTO's. Anyway, I quickly re-designed it, checking CoL and CoM position when empty:

I also discovered that when aero-breaking, the contents of the cargo bay are exposed to re-entry friction, so the cheap square batteries got replaced with a medium one that has heat tolerance of 2000 Kelvin. Also twisted slightly plane's wings so lift vector is pointing backwards and is slightly above CoM.

Ascent profile is completely different too: get to 1,000 m, point down and accelerate to 425 m/s, at sea level. Then slowly, little by little, as you gain thrust, raise AoA, 5 degrees, 7 degrees, 10 degrees, 15 degrees, etc, until rapier cuts out at 24 km and 1300 m/s.

Mission complete. If anyone interested in a youtube video, I can do that too

Edited July 3, 2016 by Zamolxes77

[Dr Farnsworth]

On 7/3/2016 at 8:23 AM, Majorjim said:

Nice work!

 If you place a part small nosecone on the rear of the rapier it will reduce the drag and give you even more dv! Open nodes cause a lot of drag.

 You should fly a full mission to Minmus and take pics!

So the nosecone on the rear of the rapier is still a thing? I figured they fixed that...

 

Zamolxes77 you have a neat design there!

Tiny craft can be the most challenging, and the most rewarding.

 

[Zamolxes77]

19 hours ago, Dr Farnsworth said:

So the nosecone on the rear of the rapier is still a thing? I figured they fixed that...

 

Honestly, I didn't see any difference, but then again, it might be something subtle. To me it seems a lot more important to carefully manage your ascent profile, since one mistake can mean you burn extra 200 m/s. Sometimes I have to learn to use those overlays that show the aerodynamic forces.

For example in some cases, I managed to peak at 1300 m/s at 24 km, in others, using same plane, barely managed 1200 m/s, and in one case 1150. Once I managed 1400 m/s at 23 km and plane disintegrated when I toggled the rapiers, probably I didn't close the intakes quick enough.

Thanks. During this challenge I learned a lot. You should see some of my old design SSTO's lol, huge mammoth with very little dV. I designed a small, rescue shuttle, with things I learned, can hold 6 people, docking port, rcs, the whole 9 yards and still has 1500 dV AFTER circularize at 75 km ! And is not much bigger than this LOL, 25 tons or so:

Big Boy:

New hotness:

[NSEP]

I fall in love with every Mini-SSTO i see. Just because its useful, cheap and its impossible for me to make. I dont like it though. I love it!