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SSTO Tylo No Refueling Or Docking


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On 11/10/2017 at 4:48 AM, JacobJHC said:

I'm pretty sure anything over 300 m/s would get too bouncy to control, Tylo isn't the flattest place.  It could potentially be done though.

A trick I used on the Mun once was to launch up a crater wall. it does become unstable but since the ground is "rising" you can get a bit more speed.

On 11/12/2017 at 7:55 AM, Zhetaan said:

The problem with ion drive is that you sacrifice a lot in terms of dead weight for not a lot of benefit.  Xenon tanks don't have good wet/dry mass ratio (the radial tank is best with 2.29; the inline tanks are 2.27) and lacking the ability to stage away the dead weight of empty tanks, you end up carrying that mass, which then takes away from mass you can use for power systems and other such.  Given the best xenon tank, the theoretical best dV for the ion engine is only 34,000 m/s:  only in this case because it is only twice the dV of the nuke using standard liquid fuel tanks.  Add to that the required power systems needed to run ions near Jool, and it becomes too much.  You'll need either a lot of batteries, a lot of panels, or a lot of RTGs, and none of that is a good solution.  Batteries are heavy, solar panels have low power generation near Jool (4% of Kerbin's efficiency), and RTGs have both of those disadvantages but with none of the benefits.  Fuel cells in lieu of solar panels might work a bit, but that adds additional parasitic mass in the form of extra tankage--although it may be possible to make use of space in slightly-oversized fuel tanks and avoid the extra dead weight (in fact, by making less of the existing weight 'dead').

The ion engine requires 8.74 EC/s to operate at full throttle.  Gigantor solar panels produce 24.4 EC/s, but at Jool (mean semi-major axis) they produce 3.91% of that, or .954 EC/s.  You'll need ten of them if you use no batteries, which adds three tonnes just in the panels.

Batteries all store charge at 20,000 EC/tonne.  To determine the needed numbers, we'll need to figure the length of burn for a given test vessel.  I'll use Tylo capture because it cannot be done with gravity assists and because it doesn't involve landing, which we already know cannot be done with ions.  A Tylo capture burn is (again going from the dV map) 1100 m/s--the real value will be more because you will, assuming a gravity assist, be entering the sphere of influence with decidedly more than the minimum orbital speed necessary to reach Tylo from low Jool orbit.  The rocket equation will give us a general answer here:

dV = Isp * g0 * ln (mw / md)

where mw and md refer not to true wet and dry mass, but rather mass before and after the burn.

1100 = 4200 * 9.80665 * ln (mw / md)

1100 = 41187.93 * ln (mw / md)

.02670685 = ln (mw / md)

1.027067 * md = mw

We can call that a comfortable 2.71% of the vessel's mass must be expelled in order to close and reduce the altitude to low Tylo orbit, or 271 kg of xenon per tonne of vessel (vessel tonnage includes unused xenon left in the tank).  The radial tanks hold 40 kg, though perhaps you would prefer fewer parts and less drag:  the PB-X750 holds 525 kg, which supplies enough that you may even be able to break orbit again.  The ion engine has a thrust of 2 kN, which can be used to get mass flow rate:

Mass Flow (kg/s) = Thrust / (Isp * g0)

= 2 kN / (4200 s * 9.80665 m/s2)

= 2,000 N / 41187.93 m/s

One newton is one kg*m/s2:

= .04856 kg/s

This is kilogrammes per second, per engine as well.  Xenon masses at .1 kg/unit, so the total fuel expenditure is .4856 units/s/engine.

Anyway, 271 kg-Xe/tonne, for an engine that expels propellant mass at .04856 kg-Xe/s, means that the total burn time must be just under 5581 s/tonne of vessel for one ion engine.  That's a 93-minute burn, per tonne.  Burn time shortens by quite a lot when the vessel is less than one tonne in mass, but that is why ion engines are best suited to probes.  Add in the 8.74 EC/s to power the engine, and we require 48777.94 EC, or more than 12 Z-4k batteries.  We can take the edge off with additional power generation, but that adds even more mass.  Remember, batteries store charge at 20,000 EC/tonne, and we've just added nearly 2.5 tonnes of them.  Immediately, we need to multiply our fuel usage and burn time by 2.5 because that is now the minimum size of the vessel.

RTGs produce .75 EC/s, so to power an ion, you need 12 of them. They mass less than the batteries, but they also create drag.  There may be an optimum balance of trade-offs, but that's before we've even considered how to store the xenon for all of this.

And none of this covers the fact that xenon cannot be used for anything else:  LFO for fuel cells can be stored in the same tanks as LF for the nuke, LF for the jet, and LFO for the landing rocket.  There's a truly great potential for mass savings just in using the same fuel for everything wherever possible.

Yeah, you have a 10 fold error here. 2% of 1000kg is 20kg, not 200kg. then the masses and burn time get more reasonable (a bit)

On 11/17/2017 at 1:01 AM, Zhetaan said:

Temporary Kerbal Maps has the highest point at about 50 degrees south latitude, at an elevation of 11,280-ish metres.  The better part is that from the map, it appears that everything in the immediate area slopes at five degrees or less.  However, there are some cliffs to the northeast, which may provide a jumping-off point for a rover-turned-rocket, if we're still entertaining that idea.  I've never visited this area, so the map is all I have right now.  In theory, Tylo's orbital speed is, where we assume circular orbits to start, GM is the standard gravitational parameter for Tylo (2.82528x10^12), Tylo's surface radius is 600,000 m, and ^(1/2) is understood as taking the square root:

At 0 m:

v = (GM / a)^(1/2)

v = (2.82528x10^12 / 6x10^5)^(1/2)

v = 2170 m/s

At 11,280 m:

v = (GM / a)^(1/2)

v = (2.82528x10^12 / 6.1128x10^5)^(1/2)

v = 2150 m/s

Which saves twenty metres per second on landing and another twenty on takeoff.  That does not sound like much but remember that we're at the absolute edge of capability:  we still don't know whether this is technically possible.  For example, one thing I intend to explore is the touch-and-go landing where the landing gear contact the ground but the vessel does not stop before taking off again.

What is the equatorial velocity of Tylo?

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1 hour ago, Antstar said:

A trick I used on the Mun once was to launch up a crater wall. it does become unstable but since the ground is "rising" you can get a bit more speed.

That's on the Mun, under low gravity. Tylo is by no means a low gravity environment.

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38 minutes ago, IMLL1 said:

I will use separations to break the rocket apart, negating the needs for pesky decouplers.

But doing that will mean the craft is not an SSTO, merely a craft with unconventional staging.

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3 hours ago, Antstar said:

Yeah, you have a 10 fold error here. 2% of 1000kg is 20kg, not 200kg. then the masses and burn time get more reasonable (a bit)

Good catch.  I don't know whether it makes the mission doable, but you're right.  Have a like.

3 hours ago, Antstar said:

What is the equatorial velocity of Tylo?

18 m/s.  Tylo is tidally locked to Jool, so that slows it down by a lot compared to moons with respectable rotation.

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Does destroying parts intentionally count as staging? :rolleyes:

If so, melting down you plane stage and used xenon tanks with rocket thrust should allow a "single stage" launch that's totally non-recoverable.

Also, are exploits acceptable?

Edited by Pds314
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Not-technically docking?

Get to orbit... Somehow.

Go to Tylo by ion engines.

Break your ship in half at Tylo.

Apollo style landing and return in one stage.

Use ion section to push the returned lander without docking to it.

Recover both the ion and lander sections.

ladders. Abuse the hell out of ladders.

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8 hours ago, Pds314 said:

Not-technically docking?

Get to orbit... Somehow.

Go to Tylo by ion engines.

Break your ship in half at Tylo.

Apollo style landing and return in one stage.

Use ion section to push the returned lander without docking to it.

Recover both the ion and lander sections.

ladders. Abuse the hell out of ladders.

You can get into the Kraken category.  

8 hours ago, Pds314 said:

oes destroying parts intentionally count as staging?

only destruction by rapid collisions

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40 minutes ago, sevenperforce said:

The point of this is to find a way to get a single-stage vehicle to Tylo and back without exploits

But this isn't mathematically possible in the game unless a kraken drive is used.

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On 11/11/2017 at 12:45 PM, Cunjo Carl said:

The numbers aren't quite as in favor of ions as they might seem. Ions create tons of drymass, enough to heavily counteract their awesome Isp on an SSTO.

 

On 11/12/2017 at 10:27 PM, Cunjo Carl said:

Most of the drymass is in those danged xenon tanks.

 

Well, there may be a small change in Ion propulsion in v1.4. It's just a little change..... Wow!!! Xenon's finally going places!

 

v_13.jpg  v_14.jpg
                      Version 1.3 Xenon tanks vs...                                Version 1.4

 

 

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6 hours ago, Cunjo Carl said:

 

 

Well, there may be a small change in Ion propulsion in v1.4. It's just a little change..... Wow!!! Xenon's finally going places!

 

v_13.jpg  v_14.jpg
                      Version 1.3 Xenon tanks vs...                                Version 1.4

 

 

All my SSTOs (except one) use ion power, this is going to help me so much. :D

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While I was investigating Single Tank Tylo I thought to do a full spreadsheet analysis of this mission taking into account that xenon tanks now have much better mass fraction.

The Rhino and LV-N are the two best engines. Of these the Rhino is easy to prove impossible: Payload fraction is minus 4 percent given the following assumptions.

  • Vessel is returned to Kerbin in one piece. No separating the craft or deliberately exploding your xenon tanks.
  • Wings, landing gear, etc. have zero mass.
  • Payload fraction to Kerbin orbit is a little under 75%. I've never seen anything this high.
  • Engines are infinitely divisible, but you can't have less than 1 engine.
  • The vehicle has at least 0.01 TWR (even at 0.01 it is impossible to perform gravity assists with perfect efficiency).
  • The best route (1011 m/s) to Jool is used. Your relative velocity to Tylo is small due to a Laythe assist.
  • The best route back is used, only 100 m/s from Tylo escape to landing back on Kerbin.
  • A 500 m/s touch-and-go Tylo landing is performed, never stopping on the surface. Descent dV is 2000, ascent and circularization dV is 2100. This is not possible without a near-infinite TWR.
  • Tylo TWR > 1.15.
  • Even though most of it is performed with the RAPIERs, Tylo landing and ascent has the same Isp as the Rhino.

I'm pretty sure the LV-N is also impossible but it requires more than these loose bounds to prove. Will update when I find out what those are (or prove myself wrong). Probably will need to fire up Mathematica for a constant altitude landing simulation.

To plug in different numbers, change values in the "Stats" or "Parameters" section of my spreadsheet, then perform the following steps:

  • For a possibility analysis, set "Guess dry mass" to FALSE and "Possibility test" to TRUE. The box will light up red for negative payload fraction (impossible) and green for positive.
  • To estimate the mass of a craft, enter something in "Payload", set "Guess dry mass" to TRUE and "Possibility test" to FALSE, and adjust the dry mass guess until it is equal to the actual dry mass.

 

 

 

Edited by Lirtosiast
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I have pondered this, and wonder - what about using a Scott Manley Gyroscopic drive to drag something from Kerbin to LTO, then use regular engines to combined with the gyro drive to land and re-orbit, then gyro your way back to Kerbin....

Could it work? My issue has been recreating the gyro drive in a way that can take the required fuel and engines to Tylo....  If you're wondering what I mean by gyro drive, then -

 

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