AS-3 Skystreak - Tier 2 R&D + Tier 3 SPH SSTO (with Tier 3 R&D upgraded variants)

[Box of Stardust]

 

Presenting the Aero-Space - 3 ‘Skystreak’, an SSTO design starting from a variant built with only Tier 2 R&D facility capability!

Dropbox: AS-3 Skystreak (Multiple Variants)

The download is a pack of a few variants, mainly Tier 3 R&D upgrades (and very slight upgrades at that), but the main show here is the AS-3F Skystreak, the original variant to actually manage to SSTO to low Kerbin Orbit, all without fancy true SSTO parts! (Although a fully-upgraded Tier 3 Space Plane Hangar is required.)

The AS-3F is controlled by a probe core, and carries no passengers; it is, however, fitted with a cargo bay that can return very small components from orbit, or, perhaps, rescue a kerbal if fitted with a command pod. It is powered by no less than four Panthers in-atmo and two Thuds for vacuum (with ~2,000m/s dV fully fueled); unfortunately these are also its weaknesses. It comes with four flush-mounted solar panels to recharge the probe core and batteries in orbit. The wingtip tanks and outboard sections are connected by fuel lines to automatically feed into the main body, although it is still recommended to manually rebalance the center of mass by transferring fuel to the frontal tanks before attempting atmospheric flight after reentry from orbit. The two small rear fuel tanks are partially drained of oxidizer, as liquid fuel is relatively scarce and the fuel budget for jet engines uses most of it or more during ascent.

Background

I spent *far* too long trying to develop a Tier 2 R&D SSTO (hours and hours); no ramjet or supersonic intakes. After 9 major iterations of a basic airframe and many more versions of those in between, I came up with this. My aim was to use it for those component recovery missions... but to be honest, I ended up doing the space program goof up of 'overcomplicate for nothing but higher cost and lots of used up time'. Still!

Oh yeah, and I can't non-physics time warp the recovery missions because there's no AGU, so it stays loosely inside the cargo bay. Also, I don't get paid for 'obtaining' the part, because technically, I never do.

For a while, it had no other name than 'AREA-9F' (Autonomous REsearch Aircraft). I was thinking over a name including 'Thunder' because it uses Thuds for its rockets (it's like, the first time I ever used Thuds lol), specifically chosen due to being the only engine able to meet the thrust requirement within weight margins. For the craft name, I eventually settled on ‘Skystreak’, which the ramjet upgrade definitely lives up to. Though, the Whiplash upgraded variants probably deserve something with ‘Thunder’...

Here's a bonus image of the 9F/3F next to the 8C, its functioning predecessor with an LV-T45, but needed a cargo bay-held ejectable fuel tank pack to make it to orbit, so not exactly an SSTO (but does have tons more delta-V in orbit than the 9F/3F; +300 compared to +100). The fuel tank pack was pretty cheap though, so it was probably still a really good design even if not 'true SSTO'. The best thing the 8C did for me though, was give me a solid numbers for fuel, thrust, and mass baselines for a functioning low-ish tech SSTO.

Lastly, some time during the design process I learned that turning off angle snap in Offset/Rotate mode allows free movement of parts. So *oh my gosh flush solar panels so satisfying*.

AS-3F Action Groups

0: Toggles all intakes (press this at start of flight)

1: Toggles Panther engines AND TOGGLES ALL INTAKES

2: Toggles Thud engines

3: Toggles Puff engines

4: Toggles cargo bay doors

9: Panther mode switch

B: Airbrakes (in addition to landing gear brakes)

Career Notes

Parts to note, for those selectively going through the tech tree and might want to use the AS-3F:

-OKTO2

-Fly-By-Wire Nose Cone

-Z-200

-J-404 Panther

-Short Mk2 Cargo Bay

-LY-35 Medium Landing Gear

-Oscar-B

-O-10 Puff

Also, there is a Small Inline Reaction Wheel fitted in the cargo bay. Advised to move this to outside where the fuel tank and rear section is, reconnect the rear section to the reaction wheel, and offset the rear section back into place; should give slightly more space in the bay, as well as avoid any possible stock aerodynamic shenanigans with the reaction wheel’s open node.

For kerbal rescue missions, I have not actually tried doing a mission, but a Mk1 Command Pod can be attached inside very snugly. I do not know how the extra mass will affect the ascent, however, as it is already a struggle (though adding a command pod in the cargo bay area will allow removal of the Small Inline Reaction Wheel). 

For component recovery missions, it’s doable for very small parts; the best I’ve done was a Panther engine floating around up in orbit (goofy other companies trying to mid-tech SSTO like me… ). However, you can’t time warp for long periods or else the two entities (craft and part) will eventually drift apart due to absence of physics during orbital warp. Atmospheric warp, however, is fine, as physics are active. Oh, also, you won’t receive the reward for ‘obtaining’ the component because technically, you never do. You just ‘recover’ it.

(A Mk1 Command Pod does fit well without clipping inside the short bay. The Small Reaction Wheel is visible in the rear of the cargo bay.)

AS-3F Ascent Profile

I have to admit- I haven’t flown the AS-3F in a while, so my memory of the correct ascent profile is not very accurate. Also, I fly with a lot of instrumentation assistance (i.e., MechJeb/Engineer readouts), so I usually fly off of information like what my vertical speed and acceleration are. My recall of the altitude and speed checkpoints is decent, but the AS-3F is fairly underpowered, so additional information definitely helps during the ascent. This is a general, inaccurate outline that is a good place to start from:

1. START-UP SEQUENCE: SAS ON, MAX THROTTLE. Press ‘0’ [CLOSES ALL INTAKES]. Press ‘1’ [ACTIVATES PANTHERS, OPENS ALL INTAKES]. (It’s taken from Cupcake’s Air-Sync from his classic SSTOs.) Caps Lock fine-control optional, but may be useful.

2. Pitch up at minimum 70m/s, wings provide definite lift at 90m/s.

3. Once airborne, Panthers stay on Dry, pitch at 25-27 degrees.

4. Afterburners ('9') at ~3,500-4,000m (dependent on speed and when it starts dropping too much), pitch up to 45-60 degrees.

5. Gradual pitch down to 10-15 degrees starting at 7,500-8,000m; by 10,000m, pitch is at 10-15 degrees.

6. Speed run. By 13km - 15km, speed should be around 700m/s.

7. Somewhere between 14km and 15km at a speed above 700m/s, activate RCS and Thuds [Press ‘2’], pitch up to 45-60 degrees without going under 600m/s speed. Turn off RCS after pitch up is secure.

8. Panthers flame out simultaneously; upon flame-out, press [1]. This shuts down the Panthers, as well as closes the intakes.

9. Uh… from here, fight to get the apoapsis up to 71,000m. I don’t remember the ascent profile from here; recommend gradual pitch down start no earlier than 35,000m, and only 5 degrees per 5,000m.

10. Circularization procedures as normal. Just make sure you don’t dip back under 70,000m… as normal.

Should all things have gone mostly well, the AS-3F should have at least 150m/s of dV in orbit for the Thuds, as well as an additional ~100m/s on the Puffs. This allows a recovery mission or a station rendezvous (though it has no docking ports, so an AGU on the station must be used or a docking port should be added (unknown how this will affect already difficult ascent profile)).

(It was built right before 1.1 came out; note the old LY-10s. They have been replaced with LY-35s, because in 1.1, LY-10s explode due to overstressing, and honestly, the LY-35s look great on it.)

Tier 3 R&D Upgraded Variants

Eight Tier 3 R&D variants are included in the download link. They share the common design of replacing the short Mk1-Mk2 adapter with the long adapter and an upgraded engine configuration to Whiplash ramjets for atmospheric flight.

-AS-3G2: Straight upgrade to the AS-3F2; dual T-1 Darts

-AS-3G2-T: Transport variant of the AS-3G2; cargo bay replaced with crew cabin, tiny docking port fitted, landing legs fitted for moon landings in tailsitter orientation

-AS-3G3: Elongated rocket fuel fuselage replaces short fuselage

-AS-3H: Dual LV-T45s, long cargo bay

-AS-3J: Dual LV-Ns, rocket fuel fuselage replaced with liquid fuel fuselage

-AS-3J-T: 3J modified to AS-3 transport configuration

-AS-3K-T: Triple LV-Ns, AS-3 transport configuration

-AS-3K2-T: Elongated fuel fuselage

Differences with AS-3F

Transport variants have the landing legs on the next open action group after the engines, and ladder toggle on the action group after that.

The LV-N variants do not have O-10 Puffs, reducing the engine action groups by one.

Ascent profile involves the same takeoff sequence, speed up to 200m/s, then pitch up to 60 degrees. Pitch down schedule is the same. Start pitch back up once 1200m/s minimum.

The higher thrust variants (LV-T45, Dart) are relatively easy to get to orbit.

The LV-N variants... an equal but different struggle from the AS-3F due to the low thrust, but high atmospheric velocity before activating the rocket engines.

Overviews

So it turns out, when an SSTO is engineered to work off of relatively underpowered engines (Panthers), as expected, when it’s given much more powerful engines (Whiplashes), it gets… well… really fast. The AS-3J climbs to 6000m at 70 degrees from the horizontal at 75-80% power. And at the speed run, a small sliver between 10km and 13km altitude, the quad Whiplashes at full throttle give the lighter variants a huge kick (topping out at around 5.15 TWR). And whereas the Panther variant is a fight to get up to speed, the Whiplash variants are a fight to... not overheat and explode, and hope there's no asymmetrical flameouts. Oh, and try and keep the thing controlled pointed straight and not get pulled up or down by aero forces.

Now, specifics. I’m going to start off with my favorite one- the AS-3J Skystreak.

(AS-3J, first flight.)

I figured oxidizer is uselessly heavy, so I took out all of the oxidizer, removed some tanks from the wingtips, replaced the short rocket fuselage with a liquid fuel one, and stuck in dual LV-Ns. Compared to the original Panther-Thud variant, it actually ends up having roughly the same fully fueled mass, in actuality being slightly lighter. It is, in fact, the lightest of the Tier 3 R&D variants, coming in at 30 tons.

The poor TWR of LV-Ns makes it a little hard for the final ascent, but if the Skystreak’s trajectory can be kicked up to launch it to 40km off of the Whiplashes, it makes it to orbit with over 1k delta-V left. But hey, no oxidizer makes logistics that much easier (or annoying, for refuel stations with oxidizer), and super efficient LV-Ns.

Quite an improvement over the Panther-Thud original prototype. (Naturally, Thuds had to be used on the AS-3F because Panthers don’t have the thrust to get the plane to a fast enough velocity, so the rocket stage had more work to do for the ascent.) Unfortunately, still not enough to do even a Minmus landing (or at least a round trip) without a refuel. With a refuel though, it’s got pretty respectable range.

The AS-3G Skystreak is a more conventional variant that uses dual Dart aerospikes instead, but it’s fairly boring otherwise. Gets up with pretty decent dV too, though (I think also about 1k, so same limitations as the 3J). This is the generalist variant, with good thrust and relatively good ISP.

(This picture is dated, and the name in the craft editor is no longer its designation.)

(Yeah, the kerbals will need to jump a bit. Also, this was before I put the docking port and boarding ladders for when the plane is landed on its wheels. And I've never actually tested the landing capability.)

The AS-3H Skystreak is a common-sense upgrade that is very comparable to the AS-3F. It's a straight upgrade using simple tech- LV-T45s, making it the only upgrade variant with gimbaling rockets. It comes with the long Mk2 cargo bay. Not built for range, but for actual orbit delivery duties with its higher thrust but lower ISP compared to dual Darts. Untested, but expected to perform as designed.

And lastly, there’s the AS-3K Skystreak. One step up from the AS-3J, it has three LV-Ns. Also untested, also expected to function well enough. The slight increase in thrust should make the ascent somewhat easier to handle. I recommend using the AS-3K2-T with more fuel.

(AS-3K-T, showing the final design of the AS-3 transport configuration.)

I'd imagine the Skystreak would also be good with RAPIERs, but I like the pure liquid fuel version too much. I'm thinking the most optimal configuration would be using quad Rapiers and have dual Whiplashes on the main body, then switch the internal fuel lines to pump rocket fuel to the outboard modules. If anyone wants to give that a shot, cool, report back.

 

Edited May 18, 2016 by Box of Stardust