Orion 1.2 - Orbiter-Forum

**eveningsky339** · 07-21-2008, 02:53 AM

I have a little issue with the Orion by sputnik. This is an interplanetary craft propelled by nuclear bombs. It does not seem to be compatible with Burn Time Calc or the "Time to Burn" display on Transx 3.12. I suspect this is because of the way the engine is modeled-- rather than constant thrust, thrust is provided by bombs, let out one by one.

I was wondering if there was any way to make this addon compatible with Burn Time Calc. I'm horrible at guessing when to start burns...

Orion 1.2

sputnik · 07-21-2008, 03:16 AM

The problem, I suspect, is not the pulsing nature -- that's mostly animation and sound effects. The problem is that the "main" thruster is effectively nonexistent -- it's only there to poll the joystick or keyboard throttle that you're used to. Then, the noise and bang happens because a thruster of THGROUP_USER is turned on.
Burn Time Calc and suchlike calculators generally aren't built to look at the USER thruster group.

I did it that way because, if the noise and visuals are tied to THGROUP_MAIN like a normal thruster, you can interrupt the cycle by jiggling your throttle around. This is bad, or at least very unrealistic.

So I see no way to change Orion to help you, and it seems unlikely your favorite aids will be redesigned to suit, either.

Andy44 · 07-21-2008, 04:48 AM

Don't despair, Burn Time Calculator MFD will still tell you your delta-V remaining! You just can't use it for auto burns.

I did a full Mars and back mission with the 10m Orion by using BTC to tell me how much delta-V I had remaining, and using TransX to tell me when I had reached my target delta-V.

Your "burns" (accelerations, actually) will not be timed as perfectly as they would with a normal rocket, but that's okay, because witht he pulsed propulsion, you won't be able to hit your target delta-V right on anyway without using a little RCS thrust for trim burns. I advise against doing these; RCS fuel runs out very quick. Better to let the error in trajectory build up and do a correction with an odd nuke charge here and there.

**eveningsky339** · 07-21-2008, 12:52 PM

Thanks to both of you. I'm a bit of a perfectionist, so little details such as precise burns tend to get to me.

agentgonzo · 07-21-2008, 02:54 PM

TransX get's the burn time from the MAIN thruster group (and I assume that BTC does it the same way too). So it won't work as Sputnik mentioned.

What you can do though, is do a test run. Get TransX/BTC to show you the Delta-V that you need. Start your burn and note how long it takes to achieve this Delta-V. Then releoad the scenario, noting this down for future use. Start your 'burn' half* of this burn-time before the Menouvre time in TransX and it will get you pretty close to the targetted trajectory.

*I think that BTC uses this assumption that you need to start half of the burn-time before the menouvre time (This is accurate for constant acceleration - vis constant mass). TransX uses a slightly more complicated and more accurate caluclation based on a variable acceleration as you burn up your fuel, leading to higher acceleration.

07-21-2008, 02:53 AM	#1
eveningsky339 Resident Orbiter Slave	Orion 1.2 I have a little issue with the Orion by sputnik. This is an interplanetary craft propelled by nuclear bombs. It does not seem to be compatible with Burn Time Calc or the "Time to Burn" display on Transx 3.12. I suspect this is because of the way the engine is modeled-- rather than constant thrust, thrust is provided by bombs, let out one by one. I was wondering if there was any way to make this addon compatible with Burn Time Calc. I'm horrible at guessing when to start burns... Orion 1.2 Orion 1.2

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07-21-2008, 03:16 AM	#2
sputnik Addon Developer	The problem, I suspect, is not the pulsing nature -- that's mostly animation and sound effects. The problem is that the "main" thruster is effectively nonexistent -- it's only there to poll the joystick or keyboard throttle that you're used to. Then, the noise and bang happens because a thruster of THGROUP_USER is turned on. Burn Time Calc and suchlike calculators generally aren't built to look at the USER thruster group. I did it that way because, if the noise and visuals are tied to THGROUP_MAIN like a normal thruster, you can interrupt the cycle by jiggling your throttle around. This is bad, or at least very unrealistic. So I see no way to change Orion to help you, and it seems unlikely your favorite aids will be redesigned to suit, either.

07-21-2008, 04:48 AM	#3
Andy44 owner: Oil Creek Astronautix	Don't despair, Burn Time Calculator MFD will still tell you your delta-V remaining! You just can't use it for auto burns. I did a full Mars and back mission with the 10m Orion by using BTC to tell me how much delta-V I had remaining, and using TransX to tell me when I had reached my target delta-V. Your "burns" (accelerations, actually) will not be timed as perfectly as they would with a normal rocket, but that's okay, because witht he pulsed propulsion, you won't be able to hit your target delta-V right on anyway without using a little RCS thrust for trim burns. I advise against doing these; RCS fuel runs out very quick. Better to let the error in trajectory build up and do a correction with an odd nuke charge here and there.

07-21-2008, 12:52 PM	#4
eveningsky339 Resident Orbiter Slave	Thanks to both of you. I'm a bit of a perfectionist, so little details such as precise burns tend to get to me.

07-21-2008, 02:54 PM	#5
agentgonzo Grounded since '09	TransX get's the burn time from the MAIN thruster group (and I assume that BTC does it the same way too). So it won't work as Sputnik mentioned. What you can do though, is do a test run. Get TransX/BTC to show you the Delta-V that you need. Start your burn and note how long it takes to achieve this Delta-V. Then releoad the scenario, noting this down for future use. Start your 'burn' half* of this burn-time before the Menouvre time in TransX and it will get you pretty close to the targetted trajectory. *I think that BTC uses this assumption that you need to start half of the burn-time before the menouvre time (This is accurate for constant acceleration - vis constant mass). TransX uses a slightly more complicated and more accurate caluclation based on a variable acceleration as you burn up your fuel, leading to higher acceleration.