DGIV geostationary orbit and back

[mike_espo]

Really like the DGIV. Nice ship.:speakcool: I use the Mk II version (200KN thrust) and default fuel. Having a difficult time getting home from the geosyncronous orbit that I put myself into. Deployed a satillite and now only have about 8% fuel left. I think I screwed up the launch, as I was not sure as to how to get into an equitorial orbit. That wasted alot of fuel as did the burns to get to a circular geosyncronous orbit. Now to save fuel for the return trip, I cannot change orbital inclination for the cape, so I will have to land somwhere near the equator.

I was able to put periapsis at 75km, and am trying to burn off energy by skimming atmosphere a number of times to get the aproapsis to where I can make a safe reentry. I am on my third orbit now and the apropapsis is down to 14M. Do I have a chance to get down safely?

Any thoughts??

thanks

 

[RisingFury]

Sure you do. Just be careful when aero-breaking. You can go to OrbitHangar.com and download AeroBreakMFD, which will help you a lot with your atmospheric reentries.

If you're still in an equatorial orbit, you can bank sideways when aero-breaking, which will force your orbit a bit sideways and you can land at Cape Canaveral again without burning more fuel.

 

[mike_espo]

Sure you do. Just be careful when aero-breaking. You can go to OrbitHangar.com and download AeroBreakMFD, which will help you a lot with your atmospheric reentries.

If you're still in an equatorial orbit, you can bank sideways when aero-breaking, which will force your orbit a bit sideways and you can land at Cape Canaveral again without burning more fuel.

Hmmm.:hmmown to 1600 lbs of propellant. I have base sync MFD and Aerobrake MFD. I thought I would have to change orbit to land at cape, Can I alter trajectory that much and won't I burn up if I bank during re entry?

 

[Zatnikitelman]

What you can try is a GTo-GEO-GTO style trajectory and change planes at APA. When you start out, go ahead and burn prograde at a node from your parking orbit till APA is at GEo altitude. Then, when you're at APA, you can either do a combination plane-change/insertion burn, or change the plane, then ont he next swing, burn into a circular orbit. Coming home, just do the reverse, drop PEA down to maybe 170km so it's stable, then swing back to APA and change the plane back to the Cape's inclination, then either try a high speed reentry and burn [again] at Pea to drop Apa into the atmosphere, or burn at PeA to drop your former APA down into the atmosphere. I'm not sure of the exact procedure you're using right now, but changine planes where velocity is lowest gives the lowest neccessary Dv.

 

[Linguofreak]

You shouldn't burn up if you bank as long as your periapsis isn't too low, and as long as you correct for sideslip.

In fact, with the right periapsis and such, you should be able to fly upside down to hold yourself in atmosphere for as long as necessary.

 

[mike_espo]

You shouldn't burn up if you bank as long as your periapsis isn't too low, and as long as you correct for sideslip.

In fact, with the right periapsis and such, you should be able to fly upside down to hold yourself in atmosphere for as long as necessary.

I already lowered PeR to 78km. ApR is 14M after 3 succsessive orbits. Won't temperature build up to where Ill be toast? DGIV is not very forgiving, I find.

 

[Linguofreak]

How close are you getting to your maximums on each pass, and what attitude (pitch and bank) are you flying in atmosphere?

 

[Arrowstar]

I already lowered PeR to 78km. ApR is 14M after 3 succsessive orbits. Won't temperature build up to where Ill be toast? DGIV is not very forgiving, I find.

You need to bring that ApR way down, I think. If it's that high you have far too much energy built up, and when you hit the atmosphere you will either skip off or, more likely, be moving far too fast and simply break up. Try a retro-grade burn at Pe and see what it does for you.

 

[mike_espo]

You need to bring that ApR way down, I think. If it's that high you have far too much energy built up, and when you hit the atmosphere you will either skip off or, more likely, be moving far too fast and simply break up. Try a retro-grade burn at Pe and see what it does for you.

Only have enough fuel for a few seconds burn.

Neat little scenario....

 

[Tommy]

You'll still have about 9km/s velocity when you hit Pe, and at that speed you'll skip unless you fly inverted, but you'll have to do it manually. The re-entry AP won't hold banks higher than 90 degrees. You may need to lower your PeA down to about 70k before the wings can generate enough lift to keep your velocity from throwing you back out of the atmosphere. Turn upside down as you get below 120k, and have the trim neutral. As you hit Pe, start applying upward (ship reference, so the trim indicator will be moving down on the scale) elevator trim to maintain VS about zero, and hold that altitude. As your V decreases, you'll be able to descend a little, by 7.5 km/s you can be down just under 65k alt, and can rotate upright. Then you can engage Pro104Spec0. Bank 90 degrees right if you are over the Western Hemisphere, or left if you are over the Eastern Hemisphere, then pitch up to 15 degrees AOA. Reduce bank to 80 - 85 degrees to maintain altitude. Once AerobrakeMFD shows you are going to pass over Canaveral, zero bank and AoA , then adjust the AoA to reach base. Depending on where you are, you may need to adjust the AoA up over 20 degrees to increase braking or below 15 to increase your range. A DGIV can go almost completely around the planet with 5 degrees AoA and 7.5 km/s of velocity.

I've re-entered a DGIV from LEO and had well over 3M crossrange. The tricky part for you may be the initial aerobrake, once you're under about 7.6K it's just a standard re-entry, and once your bank is 90 degrees or less Aerobrake will show your path pretty accurately.

A DGIV generates it's maximum lift (if you're using the AP) at 15 degrees AoA. Above that you lose lift but increase drag. Below that you lose lift and drag.

 

[dirtyname]

Turn upside down as you get below 120k, and have the trim neutral. As you hit Pe, start applying upward (ship reference, so the trim indicator will be moving down on the scale) elevator trim to maintain VS about zero, and hold that altitude. As your V decreases, you'll be able to descend a little, by 7.5 km/s you can be down just under 65k alt, and can rotate upright. Then you can engage Pro104Spec0.

Pure genius. If my DGIV is ever low on fuel, I want you in Mission Control.

 

[Tommy]

It's Agentgonzo's technique, he's the expert on aerocapture.

 

[Star explorer]

wow if i ever got in situation like that i would probly just send a rescue DGIV but i would probly use to much fuel with that also

 

[flytandem]

Hmmm... if I were stuck in geostationary and wanted to minimize the fuel to get home, I'd do like Christopher Columbus and go the other way. Actually I'm serious. How about go to the moon and back to Earth as it takes less fuel. From geostationary I think it's close to 1500 m/s deltaV to just drop the Pe to the Earth atmosphere. But to raise the Ap up to the moon is only about 1050 m/s. (save 450 m/s) The moon's gravity will do the plane change for you AND drop the Pe to the atmosphere. There would be a couple of opportunities a month to do this plus think of the view. Since there would be a full week to 10 days of coasting it should be very workable to arrive not only back at the correct latitude, but at the correct time to hit the cape.

 

[Tommy]

I wouldn't have thought of that, but it makes sense. It would take a fair amount of skill to set up that trajectory, but it doesn't need to be perfect. TransX for the initial flightplan, and IMFD's Map program (at max accuracy) to tune the Earth PE (do this with fore/aft translational RCS about 20 min after moon Pe) if needed. Direct re-entry (inverted). Flown right, at the ~10km/s velocity you'ld have coming in, you could easily get a full orbit and over 4M crossrange from a DGIV to make up for any inaccuracies.

 

[RisingFury]

You need to bring that ApR way down, I think. If it's that high you have far too much energy built up, and when you hit the atmosphere you will either skip off or, more likely, be moving far too fast and simply break up. Try a retro-grade burn at Pe and see what it does for you.

The whole point is to keep the ApR high so you barely hit the atmosphere! That will ensure you lose a lot velocity gradually and *not* break up.

 

[flytandem]

I wouldn't have thought of that, but it makes sense. It would take a fair amount of skill to set up that trajectory, but it doesn't need to be perfect. TransX for the initial flightplan, and IMFD's Map program (at max accuracy) to tune the Earth PE (do this with fore/aft translational RCS about 20 min after moon Pe) if needed. Direct re-entry (inverted). Flown right, at the ~10km/s velocity you'ld have coming in, you could easily get a full orbit and over 4M crossrange from a DGIV to make up for any inaccuracies.

I went ahead and set up a scenario with a DGIV nearly out of fuel so it must round the moon. A TransX plan shows the sling to the Earth. A maneuver is set up to match the plan. Just advance to the date of maneuver and rotate to direction and burn. I flew the mission with a MCC using TransX about the ship's Ap and watching IMFD Map to see the result in the burn to stop it when the ship Pe at Earth is 65 Km. It arrived as planned but I have no clue how to do a reentry in a DGIV. Here's the initial scenario (in bold text) with the TransX plan ready to go. It uses the latest version of TransX, 3.13 .

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GeoStationary to KSC.
END_DESC

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System Sol
Date MJD 54850.2016707755
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Ship geo2home
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TARGET geo2home
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0 54860.6770384
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AROT 0.00 0.00 0.00
PRPLEVEL 0:0.040 1:0.060 2:0.983
IDS 0:45 100
NAVFREQ 0 0
XPDR 0
;-------------------------- Skin parameters must contain directory name of skin (without space)
MeshSkin spacetech
;-------------------------- Cargo payload must contain name of config file or "none".(see doc)
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GEAR 0 0.00
AllDoorsState 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0 0.00
But1Cockpit 0 0 0 2 2 2 0 2 2 2 2 2 2 2 2 1 1 2 1 1 1 5
But2Cockpit 0 0 0 0 0 0 0 0 2 2 2 2 2 0 3 0 0 0 1 1 0 0
TransEffect 0
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LevelBatt 100.0000
Emergency_power 10000.0000
VoltageStartBus 0.0000
VoltageGen1 96.2800
VoltageGen2 96.2800
VoltageGenBus 96.0000
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CabinO2Level 21.3955
CabinCO2Level 600.0000
CabinTempLevel 21.1012
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CabinMoistLevel 36.0000
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CabinTempSetting 21.2000
CabinPressSetting 14.7000
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UMMUCREW Capt-Francois_Bowman-41-65-78
UMMUCREW -Peter_Dawson-35-69-79
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