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MitchS

SSTOs to and from Laythe

Question

Hi, all!

After a lot of help and guidance from you wonderful people over the last month or two, I went from building Single-Stage-To-Nowheres to building compact and capable Mk1, 2, and 3 spaceplanes that happily deliver station modules into orbits all over the Kerbin system--and look good to boot. With active stations and surface bases on Kerbin, Mun, and Minmus, my 30+ Kerbonaut fleet is finally put to use, and the time between transfer windows is actually as fun as the interplanetary stuff. Life is good. Thank you!

...But now a Jool window is coming up, and I want to take my new Bachelor of Science degree in Spaceplane Engineering and apply for a Masters program.

If I have a spaceplane that can take a 10t payload to LMO and return with 5% fuel left, could I just put an ISRU in one half of the cargo bay and extra fuel in the other--enough Delta V for a Jool transfer, etc--and make the Laythe trip, simple as that? Or does a spaceplane need to be designed with Laythe in mind? How does a spaceplane behave differently there? Is the ascent profile the same, with slightly different altitudes in mind, or is it fundamentally different? How do engines behave?

What did YOU learn about spaceplane design when you started going interplanetary that you think might not be obvious to a Kerbin-system SSTO builder? What did you learn when you started going to Laythe?

Thanks!

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6 hours ago, Wanderfound said:

 

Flying below 25,000m is good because you can accelerate on air-breathers. Flying above 50,000m is good because negligible drag. But between 25 and 50km is dreadful; worst of both worlds. If you're in level flight when you hit 25km, you're going to lose a huge amount of energy to drag.

 

I'll repeat what i said in the thread i linked - that 2 nuke, 1 rapier liquid fuel only design (extreme case) uses 900 dv to get from 1400m/s at 22km to  75km stable orbit.  It has >3700 dv once in orbit.  Adding 10% to it's dry mass to fit another rapier wouldn't make it more efficient, though it might enable to bump up the takeoff weight since you can get more mass through mach 1.

It doesn't have high losses because it can get enough lift between 25 and 50km without using large pitch angles, and even when keeping pitch down, it generates enough lift to quickly rise out of the thicker atmosphere.  After 90 seconds it has reached 1600 m/s and is over 35km , drag has fallen to 10kn, and we're climbing at 141 m/s.  It all depends on the design.

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2 hours ago, AeroGav said:

I'll repeat what i said in the thread i linked - that 2 nuke, 1 rapier liquid fuel only design (extreme case) uses 900 dv to get from 1400m/s at 22km to  75km stable orbit.  It has >3700 dv once in orbit.  Adding 10% to it's dry mass to fit another rapier wouldn't make it more efficient, though it might enable to bump up the takeoff weight since you can get more mass through mach 1.

It doesn't have high losses because it can get enough lift between 25 and 50km without using large pitch angles, and even when keeping pitch down, it generates enough lift to quickly rise out of the thicker atmosphere.  After 90 seconds it has reached 1600 m/s and is over 35km , drag has fallen to 10kn, and we're climbing at 141 m/s.  It all depends on the design.

Each to their own, certainly. :)

do like my hotrods, though. And they've definitely got the range to get wherever they need to go.

Lotsa nuke and lotsa wing vs lotsa thrust and minimal wing; alternate build philosophies. They both work; option 2 is easier to get to orbit, option 1 may be a bit easier on atmospheric landings.

 

 

 

Edited by Wanderfound

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Any word from the Skunk Works @MitchS ?

After a mammoth sleep session,  I found time to actually fly my version of your craft above 2000m today (surely the most untested thing i ever put on KerbalX :blush:).  Also someone had asked for more pictures, so here we go -

20170115152812_1_zpstpw0ngby.jpg

Mach 1.5 baby

20170115153518_1_zpsdp6pfeez.jpg

I kept feeding in nose down trim to stop it climbing over 22km during the speedrun.  At 1500 acceleration started to slow down, so set Prograde, pressed ALT + X to remove all the nose down trim, and activated the nukes.  After hearing the "phut" of the jets flaming out, we go close cycle mode and kiss goodbye to 440 units of oxidizer and 360 LF in the blink of an eye.  It accelerates us from 1600 to 1900 though, which is enough to guarantee departure from the atmosphere.

20170115153818_1_zpslntslp8n.jpg

So,  we got to space on our first attempt, with 4377 delta V remaining in low Kerbin orbit.

Issues discovered - 

  • The nose gear is set to "steering : inverted".  No wonder it was so hard to keep straight on the runway !
  • Reaction wheel on the nose too vulnerable to heat.   With RTG power, no need for all those batteries, i think such things are best off inside cargo bays anyway, that way all external parts have 2400k or more heat tolerance.

Having made it to orbit,  my thoughts return to the mining setup.  The big question : are we going to include an orbital survey scanner or not?    They are very light, but utterly freaking huge.  It's almost the length of a long mk2 cargo bay, and will clip through the walls of the bay when deployed.  Honestly, it is possible to get by without one. If really unlucky it is possible to land where no ore exists, then just roll a few hundred metres across the ground and the concentration will be better.  But, it seems carrying an orbital survey satellite is the intended way of doing things.   This requires a significant stretch of the cargo bay so am investigating this branch before refining the ship any further.

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I tend to agree that the orbital scanner belongs on a probe that you send ahead to the target CB. Since it needs to be in a polar orbit at a particular altitude, operates once, and then can leave immediately for another moon -- while the main lander usually does better in an equatorial orbit. So the orbital needs of the two systems don't match.

And I like to have plenty of batteries on anything that's going to be doing a lot of drilling & conversion. They can charge up slowly while you are cruising around doing science, and then have enough power to get your equipment up to full operating temp. Since you have enough wing on here (and can even have some fuel for retroburning), you won't have any trouble at all with reentry heating. So I would leave the batteries outside, myself. Don't need to use up precious cargo space with them.

 

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The mid-range orbital scanner is almost as good, and much more compact:

ULVMd7f.jpg

 

Or you could just go for the ground-only scanner, and use the room for a materials bay instead.

This one is using two fuel cell arrays tucked above the ISRU. The fuel consumption is irrelevant, as you only ever activate them while you're mining & refining; a pair of solar panels cover normal power usage. The fuel cell arrays also provide all the power storage needed.

Edited by Wanderfound

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3 hours ago, Wanderfound said:

The mid-range orbital scanner is almost as good, and much more compact:

 

Or you could just go for the ground-only scanner, and use the room for a materials bay instead.

 

I know that before the last update, the narrow band scanner would not return any data, and tell you that you need to do an orbital scan first, if you tried to use it on a body that hadn't first been scanned with the big 'un.    Has this changed with all that new Kerbnet/Anomaly scanning stuff ?

@bewing  Actually I have quite a bit of room in the cargo bay for batteries, because a lot of the stuff we need is 1.25m but it's in a mk2 bay, which leaves space at the sides for radial mounted batteries.  There's quite a bit of wasted space in fact.   Whilst i'm willing to put cones on the back of engines,  I try to avoid clipping cargo bay equipment and all those survey scanners and antennas are awkward shapes.   All the mk2 fuel tanks have been replaced with additional cargo bay,  which is now twice the length of the original ship.    Just call it additional realism/challenge, like the provision of a mk2 crew cabin (extra living space for the crew).

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11 hours ago, AeroGav said:

I know that before the last update, the narrow band scanner would not return any data, and tell you that you need to do an orbital scan first, if you tried to use it on a body that hadn't first been scanned with the big 'un.    Has this changed with all that new Kerbnet/Anomaly scanning stuff ?

It won't build you a map, but it will tell you what you're flying over in a low orbit.

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Hey everyone. Thanks for the good discussions. I haven't been able to run KSP since my test flights last Wednesday--real life has been an enormous nuisance lately! Fortunately, my job allows a certain degree of forum browsing throughout the workday without cutting into productivity...

...But I can't wait to sit down and finish this thing up with all of your good advice.

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