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How to get into low Kerbol orbit with sane design?

Cesrate

By Cesrate
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Cesrate

Cesrate

Posted
Posted (edited)

Title is the question.

Well the ÃŽâ€v is beyond 30,000 m/s and according to Chiolkovski Function, despite of gravity assist and staging, the initial mass / dry mass will be (ÃŽâ€v=Isp•g•ln(mi/md)):

Antimatter Rocket(Currently not exist in KSP): 1.0030-1.0003

VASIMR(Currently not exist in KSP; Isp 12,000s): 1.29

PB-Ion Ion Rocket: 2.07

LV-N Nuclear Thermal Rocket: 45.72

LV-909/Aerospike/Rockomax "Poodle": 2543.49

LV-T30/LV-T45: 3886.04

Solid Rocket Booster BACC: 205338.66

Little Separation SRB: 1910630985506.53 (LOL)

Any suggestion?

Edited by Cesrate
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zarakon

zarakon

Posted
Posted

Yeah, I got really close to the sun using something like Temstar's. LV-N stage with drop-tanks, followed by an ion stage with drop-tanks. Be aware that when you're really close to the sun, solar panels are super efficient, so you don't need many of them to run an ion engine at full power.

I also recommend using DEADBEEF's dynamic warp mod to do this stuff at x8 or x16 speed, because these burns take a loooooooong time

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Specialist290

Specialist290

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Posted

A good number actually never leave Earth orbit; they're just pointed at the Sun to take readings.

Of the ones that are (or were) intentionally placed in heliocentric orbits:

* The two STEREO probes were deliberately placed in orbits slightly inwards and outwards from the Earth to provide stereoscopic images.

* WIND, SOHO, and ACE are all currently hanging out at Sun-Earth Lagrange Point 1.

* Helios 1 and 2 are the probes that got the closest to the Sun with a perihelion of ~0.29 AU, but their orbits are highly elliptical, reaching all the way back out to Earth's orbital trajectory.

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chainedlupine

chainedlupine

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Posted (edited)

40 tons LV-N to get close to the sun? Heh. I like that.

And ROFL, it's more than a "bit." You're moving very fast. I don't have numbers handy but I am sure it's well over 15,000 m/s for a circularized orbit around the sun.

Update: Durp, Cerate mentioned the number in their post. 30,000 m/s dV.

Edited by chainedlupine
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UmbralRaptor

UmbralRaptor

Posted
Posted

Well the ÃŽâ€v is beyond 30,000 m/s and according to Chiolkovski Function, despite of gravity assist and staging, the initial mass / dry mass will be (ÃŽâ€v=Isp•g•ln(mi/md)):

PB-Ion Ion Rocket: 2.07

LV-N Nuclear Thermal Rocket: 45.72

The PB-Ion is clearly the winner, though 30+ km/s should be doable with an asparagus staged LV-N. The poor mass ratio of the xenon tanks is an issue, but should be workable with a multistage design. You're likely to end up with hour long burns at 4x timewarp, no matter what.

A mass ratio of 46 means that a nuclear design is enormously sensitive to payload mass. I hope you don't need to bring heavy instruments. Here's a design that should get ~29 km/s, but starts out at 190 tonnes, and will need to be lifted into LKO.

highdV0191A_zpsf7229904.png

Umm… What position are the real-world Sun exploration probes in? We don't have so many NTRs and ion rockets right…
Often ellliptical orbits that take them near the sun briefly (eg: Helios 2, Ulysses), or orbits with earth-like semi-major axes and eccentricities (eg: ACE, Stereo-B, SOHO). The Earth-Sun L1 point sees some use.
46 ton LV-N ship sounds pretty reasonable.
Mass ratio, not GLOW.
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Temstar

Temstar

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Posted

This got me thinking though, if we were trying to place a probe to as low of a circular Kerbolar orbit as possible for a given delta-V what method would we go for?

1. Direct ejection from Kerbin SOI, then hohmann transfer orbit then circularise.

2. Kerbin -> Eve, powered slingshot from Eve, circularise

3. Kerbin -> Jool, powered slingshot from Jool, circularise

In additional, if we have the infrastructure set up at Eve or Jool we could also go for:

4. Kerbin -> Eve transfer, refuel at Low Eve Orbit, ejection from Eve SOI, hohmann transfer orbit then circularise

5. Kerbin -> Jool transfer, refuel at Low Jool Orbit, ejection from Jool SOI, hohmann transfer orbit then circularise

Which method would get us the lowest Kerbolar orbit?

(Now if only we could "aerobrake" using Kerbol's corona)

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UmbralRaptor

UmbralRaptor

Posted
Posted

Option 1 is likely out. You can save several km/s by doing a bi-ellptic transfer. Options 2 and 3 vs bi-elliptic are more interesting. I suspect that an unpowered flyby of Jool exists that will get your periastron sufficiently low. Provided you don't lose anything in course corrections (ha!), this could save ~700-2000 m/s. An Eve flyby may offer larger savings, as setting that up from a 70 km Kerbin orbit takes ~880 m/s less than a Jool flyby.

For option 4, I would again lean bi-elliptic. For option 5, I wonder if Jool escape would add too much ÃŽâ€V cost. Maybe Eeloo near its apoapsis?

At the other end, it looks like escape velocity at the star's surface is ~94.6 km/s, and a circular orbit is ~66.9 km/s. Due to the high eccentricity, I would expect all orbits to start out near the escape one before circularization burn(s). This may have been where Cesrate's 30 km/s figure came from.

Depending on the method used, call it 35-40 km/s from Kerbin's surface to a star-scraping orbit. (With the first 4.4-7 km/s forced to use relatively high TWR engines)

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SunJumper

SunJumper

Posted
Posted
Option 1 is likely out. You can save several km/s by doing a bi-ellptic transfer. Options 2 and 3 vs bi-elliptic are more interesting. I suspect that an unpowered flyby of Jool exists that will get your periastron sufficiently low. Provided you don't lose anything in course corrections (ha!), this could save ~700-2000 m/s. An Eve flyby may offer larger savings, as setting that up from a 70 km Kerbin orbit takes ~880 m/s less than a Jool flyby.

For option 4, I would again lean bi-elliptic. For option 5, I wonder if Jool escape would add too much ÃŽâ€V cost. Maybe Eeloo near its apoapsis?

At the other end, it looks like escape velocity at the star's surface is ~94.6 km/s, and a circular orbit is ~66.9 km/s. Due to the high eccentricity, I would expect all orbits to start out near the escape one before circularization burn(s). This may have been where Cesrate's 30 km/s figure came from.

Depending on the method used, call it 35-40 km/s from Kerbin's surface to a star-scraping orbit. (With the first 4.4-7 km/s forced to use relatively high TWR engines)

With ion engines, as you must burn significantly before/after periastron, the required delta-v goes up maybe 10%.

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SunJumper

SunJumper

Posted
Posted
How close can you actually get to Kerbol without being incinerated/crashing into the "surface"? I remember reading it didn't actually have any collision meshes or even a surface or anything, but I don't know if that's still true.

When you get below 1338m, you overheat and die.

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