Question

I am playing around with a 2.7 ton SSTO in sand box.

The craft is 3 Oscars, a Spark, a basic solar panel, an octo2, a small inline reaction wheel and a small nose cone it has 3594 m/s dV which I'm sure I can get into orbit.

I have comnet turned off, which means that require signal for probe control is off and no need for extra ground stations.  yet I'm still losing control of the probe at 70km up.

I've even tried with comnet on and extra ground stations enabled.  I thought the octo2 would have enough internal antenna to cope with LKO?

What settings do I use to completely ignore the need for antena?

My bad it's 880kg .. the 2700 was the cost :D

 

Edited by NewtSoup

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There are several possible reasons but one i find more likely is that you simply run out of power. Your core stores only 5 units and uses 1.08 per minute+ your reactionwheel. If your Solarpanel is facing the wrong direction it might not produce any /to little power.

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I'm also like 99.99% sure that engine doesn't have an alternator, so that's biting you too.

It does gimble though, so you may be able to toss the reaction wheel.

Edited by Geonovast

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Yeah it was the lack of leccy!

Rookie Mistake.. I should know bettter :)

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Adding a 100 Battery solved the issues!

The spark absolutely does not have an alternator.  One launch I got stuck on full throttle :) 

Still not made it to stable orbit on 3600 DV. Need to learn to fly that perfect trajectory!

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Quick redesign

4 Oscars
4 Basic Fins
1 battery
1 solar panel
1 okto 2
1 small nose cone
1 spark
1 steerable nose wheel as landing gear!
1165 kg

Cheated a bit clipping the nose wheel into the body but I imagine the engineers just hacksawed off the unnecessary bits.

Still didn't get orbit with 3642 dV

But did at least land half a ship! Only lost the 2 rear tanks the spark and 2 fins... Landed a bit tail heavy but it glides really quite well!.

Of course an SSTO this small with such small tolerances on fuel and therefore payload has no real use beyond amusement value.

Edited by NewtSoup

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2 hours ago, NewtSoup said:

Still not made it to stable orbit on 3600 DV. Need to learn to fly that perfect trajectory!

Keep in mind that with a light tiny craft like that, drag tends to have a relatively big effect. You will probably expend more dV than expected even on an optimal trajectory.

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Made it to a 89,912 / 70,141 m orbit with:


4 Oscars
3 Basic Fins
1 battery
1 solar panel
1 okto 2
1 small nose cone
1 spark
1 steerable nose wheel as landing gear!
1,095 kg on the pad.

637 m/s still in the tanks.

XN4lrP.pngAsygIh.pngSW28xY.png

 

Edit: Went a bit more reductionist.

Made it to a 89km / 76km orbit with:


3 Oscars
3 Basic Fins
1 battery
2 solar panel
1 okto 2
1 small inline reaction wheel
1 small nose cone
1 spark
1 steerable nose wheel as landing gear!
895 kg on the pad.

7DW7GP.png

147 m/s in the tanks.

 

Adding the reaction wheel lets you ditch the fins.  That landing gear is killing you.

 

Edited by Geonovast

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Screenshots (F1) would help, but smaller rockets feel the aero drag more than big rockets. Also, it's hard to get an accurate dV reading when one engine is going from sea-level all the way to vacuum. ISP goes down the deeper in the soup you are (from 320s vac to 270s ASL for the Spark), and your dV reading is for vacuum. Using KER? There's a button for an atmo-dV readout, which for your rocket gives about only 3048m/s ASL. By 10km your ISP is up to 311s, and almost 319s by 20km. So it's hard to say just how much dV you actually have. You probably have enough, but your margin is even thinner than you think.

The other issue is drag. Having bits sticking out from the side adds a lot of parasitic drag to such a small rocket. For an extra 5kg, you can replace the radial z-100 battery with an inline z-200, saving drag there. The landing gear you don't really need, shaving off 45kg. Replacing the single SP with 2 OX-STATs (for symmetry) drops the weight to 1110kg with a hair over 4km/s of vac-dV. You could go with 3 fins (fine for the passive basic fins, but not recommended for steerable fins), as Geonovast suggested, to save another 10kg, adding another 74m/s

Edit: For that matter, you don't even need fins. I used 3 oxstats as fins and it worked fine. The engine gimbal is enough to fly without any fins at all, as long as you don't venture far off prograde. I made orbit with no fins or reaction wheels after flipping out a few times.

 

Edited by StrandedonEarth

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I've made it to orbit with this:

a3nfxwp.png

it's an untidy orbit and I don't have much dV left but it will get me back into the atmosphere.

The idea is that I want to land it again.  So now I have an extra oscar and 2 nosewheels.

I'm confident i can land it.  Maybe not at the KSC, the orbit isn't circular enough for me to pick a landing spot. But I can land it.  Better Pilots could probably land it on the runway with a tidier orbit.

 

Oh this one is just under 1.5 tons on the landing pad

5 oscars

Edited by NewtSoup

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1 minute ago, NewtSoup said:

The idea is that I want to land it again

Ahhh.  Did not realize that was the case.

I'm curious how it does on re-entry.  Those basic fins hate heat.  I'll be amazed if you still have them when you come back down.

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I'll let you know.. it did ok on a suborbital flight out to 90km and back down

 

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Made it through re-entry just fine!
x9qpVT4.png

Nice approach to level desert

BF3dIRM.png

 

But flared my landing too soon.  Lost my horizontal and fell like a brick the last 30 meters and exploded.

Time for a bath I think.  Wash the probe debris and fuel residue off me.

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5 hours ago, Geonovast said:

I'm curious how it does on re-entry.  Those basic fins hate heat.  I'll be amazed if you still have them when you come back down.

Should work fine, it's a very light craft and will slow down quickly in the high atmosphere. They'll only burn off if you stick them on something heavier.

That's a very cool little craft by the way @NewtSoup. Making a rocket-powered recoverable SSTO that small isn't easy at all.

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9 hours ago, Brikoleur said:

Should work fine, it's a very light craft and will slow down quickly in the high atmosphere. They'll only burn off if you stick them on something heavier.

That's a very cool little craft by the way @NewtSoup. Making a rocket-powered recoverable SSTO that small isn't easy at all.

Thank you @Brikoleur, it's been fun getting it to work.

Final attempt - Made it to a stable 71km / 79km orbit with just 8m/s dV left.    I was able to deorbit with a PE of 60km with that 8m/s

Landed in water rather than on land but vertical speed was about 4m/s and horizontal was less than 40 m/s so I am calling that perfectly landable.

Ot6I6Bo.png

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