Hello, this is my second thread. I am glad to see kind members helping and teaching me in my first thread. Hopefully, the same matter repeats in this thread.
My problem concerns with the aerobrake technique employed in most cases when fuel is limited or maybe we want to utilize the Martian atmosphere for some beneficial uses. I have been to Mars successfully for several times, owing to the guidance of the IMFD. However, IMFD doesn't offer any aerobrake programs. Basically, you (more accurately, I) set the Planet Approach program and ensure your PeA value is some 200 km if you don't plan to utilize Martian atmosphere for aerobraking. I opted for a lower PeA value, some 30-40 km. That is my initial plan, dip down into the atmosphere and watch the atmospheric drag in action. Then, conduct the Orbit Insert program.
However, weird things happen. I actually tried both values; the 200 km PeA first then I reopened the scenario and set PeA to 40 km in the second instance. (I quick-saved the scenario just before setting the PeA value in the Planet Approach program in the IMFD)
Talking about the first case. After setting the PeA value to 200 km in planet approach program. I engaged autoburn (hereinafter abbreviated as AB) and I watched the orbit trajectory in the Orbit MFD slightly changed. Yeap, successful burn. Then, I switched my MFD to Orbit Insert MFD and get prepared for another AB. I accelerated time until reaching the 300 km altitude mark. Then, slowly I watched my altitude dropped and engage AB. I still need to wait until T-value counted zero. However, just before T-value approached zero. My DG turned prograde suddenly (without any autopilot program engaged). Then, I saw it. My altitude dropped below the threshold and I switched to external view.
Aerobrake occured. I saw the bright flames surrounding my DG and switched back to 2-MFD view. The eccentricity indeed dropped. Velocity was decreasing. Not bad, or so I taught. The bad news came when I don't take control of the DG, allowing it to simply hit smack-dab onto the ground. Then, due to DG's high residual speed. It took off again and whosh. It was back off into space. Luckily, I was able to quickly engaged retrograde autopilot and immediately burn to reduce eccentricity to nearly zero. I flew to base manually, with many trials and error because I ignored the numbers, distance and time, so I overshot many times, watching Olympus Base sliding past my side.
The second hard try is equally frustrating. Anyway, it was a whole lot better, since lowered PeA value took me into the atmosphere faster than the previous trial. I became smart by manipulating controls. Once I saw the flame, I quickly engaged horizon autopilot with prograde-facing direction. This time, I turned off RCS and used aileron to pitch down and up occasionally, not wanting to let DG wandered off into space or crashed onto ground once again. I successfully maintained altitude at nearly 15 km. Still watching DG bleeding off energy, I realized that I could at least allow DG to enter a highly eccentric orbit, but definitely captured by Martian gravity.
This time I was successful, albeit further periapsis negative delta-V burn was unavoided. After telling a long story, it is time to ask some questions, directed to the experts of course.
I would like to know what is the optimum height to conduct aerobrake on Mars. Is it as low as 14 km or maybe the atmospheric density may be higher a bit at higher altitudes? Also, is it possible to enter a nearly circular orbit simply by using aerobrake without any periapsis retrograde burn?
Edit: one more question: What about the orientation of DG? I engaged retrograde autopilot as DG has high Lift to Drag Ratio. However, Dg failed to orientate itself properly when it was in the atmosphere, some sort of mysterious forces seem to act on it, causing it to reorientate its position. What is that mysterious force? Any explanation behind?
Please share some of your useful tricks in entering Martian orbit using aerobrake. I plan to demonstrate aerobrake technique to school students using Orbiter. Mars is a good example. (Background: I participated in my school Science and Math Fair. I plan to use Orbiter to demonstrate different orbital maneuvers to them)
Thanks for sharing.
Regards,
Nicholas
---------- Post added at 02:46 PM ---------- Previous post was at 09:48 AM ----------
It seems like nobody cares my thread. I am waiting for your kind sharing of knowledge and experience.
Nicholas.
My problem concerns with the aerobrake technique employed in most cases when fuel is limited or maybe we want to utilize the Martian atmosphere for some beneficial uses. I have been to Mars successfully for several times, owing to the guidance of the IMFD. However, IMFD doesn't offer any aerobrake programs. Basically, you (more accurately, I) set the Planet Approach program and ensure your PeA value is some 200 km if you don't plan to utilize Martian atmosphere for aerobraking. I opted for a lower PeA value, some 30-40 km. That is my initial plan, dip down into the atmosphere and watch the atmospheric drag in action. Then, conduct the Orbit Insert program.
However, weird things happen. I actually tried both values; the 200 km PeA first then I reopened the scenario and set PeA to 40 km in the second instance. (I quick-saved the scenario just before setting the PeA value in the Planet Approach program in the IMFD)
Talking about the first case. After setting the PeA value to 200 km in planet approach program. I engaged autoburn (hereinafter abbreviated as AB) and I watched the orbit trajectory in the Orbit MFD slightly changed. Yeap, successful burn. Then, I switched my MFD to Orbit Insert MFD and get prepared for another AB. I accelerated time until reaching the 300 km altitude mark. Then, slowly I watched my altitude dropped and engage AB. I still need to wait until T-value counted zero. However, just before T-value approached zero. My DG turned prograde suddenly (without any autopilot program engaged). Then, I saw it. My altitude dropped below the threshold and I switched to external view.
Aerobrake occured. I saw the bright flames surrounding my DG and switched back to 2-MFD view. The eccentricity indeed dropped. Velocity was decreasing. Not bad, or so I taught. The bad news came when I don't take control of the DG, allowing it to simply hit smack-dab onto the ground. Then, due to DG's high residual speed. It took off again and whosh. It was back off into space. Luckily, I was able to quickly engaged retrograde autopilot and immediately burn to reduce eccentricity to nearly zero. I flew to base manually, with many trials and error because I ignored the numbers, distance and time, so I overshot many times, watching Olympus Base sliding past my side.
The second hard try is equally frustrating. Anyway, it was a whole lot better, since lowered PeA value took me into the atmosphere faster than the previous trial. I became smart by manipulating controls. Once I saw the flame, I quickly engaged horizon autopilot with prograde-facing direction. This time, I turned off RCS and used aileron to pitch down and up occasionally, not wanting to let DG wandered off into space or crashed onto ground once again. I successfully maintained altitude at nearly 15 km. Still watching DG bleeding off energy, I realized that I could at least allow DG to enter a highly eccentric orbit, but definitely captured by Martian gravity.
This time I was successful, albeit further periapsis negative delta-V burn was unavoided. After telling a long story, it is time to ask some questions, directed to the experts of course.
I would like to know what is the optimum height to conduct aerobrake on Mars. Is it as low as 14 km or maybe the atmospheric density may be higher a bit at higher altitudes? Also, is it possible to enter a nearly circular orbit simply by using aerobrake without any periapsis retrograde burn?
Edit: one more question: What about the orientation of DG? I engaged retrograde autopilot as DG has high Lift to Drag Ratio. However, Dg failed to orientate itself properly when it was in the atmosphere, some sort of mysterious forces seem to act on it, causing it to reorientate its position. What is that mysterious force? Any explanation behind?
Please share some of your useful tricks in entering Martian orbit using aerobrake. I plan to demonstrate aerobrake technique to school students using Orbiter. Mars is a good example. (Background: I participated in my school Science and Math Fair. I plan to use Orbiter to demonstrate different orbital maneuvers to them)
Thanks for sharing.
Regards,
Nicholas
---------- Post added at 02:46 PM ---------- Previous post was at 09:48 AM ----------
It seems like nobody cares my thread. I am waiting for your kind sharing of knowledge and experience.
Nicholas.
Last edited: