KAGUYA lunar explorer (aka SELENE) |
KAGUYA lunar explorer (aka SELENE) |
Jun 6 2007, 08:29 PM
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#1
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Member Group: Members Posts: 370 Joined: 12-September 05 From: France Member No.: 495 |
SELENE has now a nickname : KAGUYA.
http://www.jaxa.jp/topics/2007/06_e.html Edit : And Emily searched for the origin of the name http://www.planetary.org/blog/article/00000996/ |
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Oct 7 2007, 01:32 AM
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#2
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Member Group: Members Posts: 279 Joined: 19-August 07 Member No.: 3299 |
A new update from Kaguya. It has already performed the 3rd LOI.
The First LOI: Injected orbit Apogee altitude 11,741 km Perigee altitude 101 km Period 16 hours 42 minutes The second LOI: Apogee altitude 5,694 km Perigee altitude 108 km Period 7 hours 53 minutes The third LOI: has already conducted. There are still three more. More details KAGUYA (SELENE) Lunar Orbit Adjustment Maneuver (LOIx) Just a curiosity, how does the spacecraft able to lower the Apogee? Trying to understand it, it is done by firing the rocket when the spacecraft is reaching the apogee so that the next loop will go slower and thus reducing its next apogee altitude and continues until reaching the desired altitude? |
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Oct 7 2007, 02:10 AM
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#3
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Member Group: Members Posts: 163 Joined: 16-March 05 From: Oakville, Ontario, Canada Member No.: 201 |
Just a curiosity, how does the spacecraft able to lower the Apogee? Trying to understand it, it is done by firing the rocket when the spacecraft is reaching the apogee so that the next loop will go slower and thus reducing its next apogee altitude and continues until reaching the desired altitude? Simple Really, The simplest way to raise or lower the perigee or apogee is to do a rocket firing at opposite position you want to change. ie. to lower apogee you decrease speed at perigee. or to raise apogee you increase speed when at perigee. etc... so the burn doesn't change the current position..it affects the opposite side of the orbit. Efficiency issues using fuel resources sometimes has multiple perigee burns to increase the apogee to the required size..which is why I believe the probe did several orbits around the Earth. (I may be wrongabout why multiple burns though ) cheers jb |
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Oct 9 2007, 11:43 AM
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#4
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
Efficiency issues using fuel resources sometimes has multiple perigee burns to increase the apogee to the required size..which is why I believe the probe did several orbits around the Earth. (I may be wrongabout why multiple burns though ) A couple of factors play in. One, ideally the delta-V should be impulsive (i.e. instantaneous, with infinite thrust) But that means infinite structural loads, and a big engine. With a real engine, the thrusting must be conducted over a finite time, i.e. a finite orbital arc. If the vehicle is spin-stabilized, and the arc is long, then the engine suffers a cosine loss in useful thrust at the ends of the arc, and so it can be more efficient to split the burn up into smaller ones (each with lower losses). There can also be issues of orbit determination or safety (e.g. that should a burn fail part way through, you arent left in some catastrophic orbit - sometimes splitting it up can avoid danger zones) but that is less likely here. |
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