IPB

Welcome Guest ( Log In | Register )

50 Pages V  « < 30 31 32 33 34 > »   
Reply to this topicStart new topic
Akatsuki Venus Climate Orbiter
pandaneko
post Sep 8 2011, 10:02 AM
Post #466


Member
***

Group: Members
Posts: 817
Joined: 17-April 10
From: Kamakura, Japan
Member No.: 5323



JAXA HP is saying;

OME was fired for 2 seconds at 11:50 (JST) on 7 September as planned in order to establish quantitatively external disturbances (such as lateral propulsion) and the telemetry data is now being analysed.

The 20 seconds firing planned for 14th will be used to verify the attitue control logic system.

P

Go to the top of the page
 
+Quote Post
Paolo
post Sep 9 2011, 11:43 AM
Post #467


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



Pandaneko, can you confirm the Google translation of today's JAXA release that the measured acceleration was less than expected?
Go to the top of the page
 
+Quote Post
pandaneko
post Sep 9 2011, 02:00 PM
Post #468


Member
***

Group: Members
Posts: 817
Joined: 17-April 10
From: Kamakura, Japan
Member No.: 5323



QUOTE (Paolo @ Sep 9 2011, 08:43 PM) *
Pandaneko, can you confirm the Google translation of today's JAXA release that the measured acceleration was less than expected?


Yes, I confirm that the measued acceleration was less than expected. As a result the planned firing of 20 seconds on 14th will be shortened to 4 seconds in order to re-check the status of OME. Apparently, there is no change to Akatsuki after the first firing.

What does all this mean? Someting fell off again before the first firing? Oxidiser leak? Perhaps, helium, less of it remaining?

P
Go to the top of the page
 
+Quote Post
Paolo
post Sep 9 2011, 02:31 PM
Post #469


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



if the "bell" of the thruster is physically damaged, gases would not expand the way they should, which could explain the "loss of acceleration"
Go to the top of the page
 
+Quote Post
Paolo
post Sep 10 2011, 12:34 PM
Post #470


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



according to the NASAspaceflight forum the engine provided only 13 p.c. of the expected thrust. very bad news...
Go to the top of the page
 
+Quote Post
pandaneko
post Sep 10 2011, 12:53 PM
Post #471


Member
***

Group: Members
Posts: 817
Joined: 17-April 10
From: Kamakura, Japan
Member No.: 5323



QUOTE (pandaneko @ Sep 9 2011, 11:00 PM) *
Yes, I confirm that the measued acceleration was less than expected. As a result the planned firing of 20 seconds on 14th will be shortened to 4 seconds in order to re-check the status of OME.


My apologies. Next firing will be "about" 5 seconds, not 4 seconds.

P
Go to the top of the page
 
+Quote Post
pandaneko
post Sep 11 2011, 02:18 PM
Post #472


Member
***

Group: Members
Posts: 817
Joined: 17-April 10
From: Kamakura, Japan
Member No.: 5323



I am no longer sure if Akatsuki will be able to be of any use because today's Yomiuri newspaper says;

"the propulsion measued at the first firing was one ninth of the expected value"

I do not know how much fuel there still is left, but my gut feeling is that Akatsuki will run out of fuel. Sad...

P
Go to the top of the page
 
+Quote Post
Paolo
post Sep 11 2011, 03:46 PM
Post #473


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



they can still make it to venus using the RCS thrusters, but the mission will be shorter
Go to the top of the page
 
+Quote Post
pandaneko
post Sep 15 2011, 01:24 PM
Post #474


Member
***

Group: Members
Posts: 817
Joined: 17-April 10
From: Kamakura, Japan
Member No.: 5323



re second firing test on 14th, same as the 1st, propulsion less than expected (no value given in today's JAXA release). JAXA will think about what to do next based on these lower values.

They may announce something more concrete.

P
Go to the top of the page
 
+Quote Post
nprev
post Sep 16 2011, 02:33 AM
Post #475


Merciless Robot
****

Group: Admin
Posts: 8783
Joined: 8-December 05
From: Los Angeles
Member No.: 602



sad.gif ...thanks for the update, Pandaneko.

The (possibly) good news here is that the engine is still capable of generating at least SOME delta-V, so instead of merely jettisoning it & relying entirely on the RCS some productive maneuvers seem possible at first glance.

Big unknown here is whether the thrust vector is still aligned properly (thinking nozzle damage here) or perhaps even stable & predictable.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
tanjent
post Sep 16 2011, 05:20 AM
Post #476


Member
***

Group: Members
Posts: 214
Joined: 30-December 05
Member No.: 628



I recall contingency plans to jettison excess oxidizer, but I believe that fuel not burned in the main engine can be burned in the RCS. (The engineering details are far from clear to me, because chemically speaking oxidizer should either be required or not required, regardless of what engine is being used.) If however, the excess fuel is somehow usable by the RCS then the question becomes where it can be used most efficiently in terms of changing the course of the spacecraft. If the OME is 87% less efficient that originally planned, then unless the RCS is even less efficient that that, it probably doesn't make sense to burn any of the remaining fuel in the OME.
Go to the top of the page
 
+Quote Post
Paolo
post Sep 16 2011, 05:31 AM
Post #477


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



the OME is a bi-propellant thruster, i.e. it generates gas by the spontaneous combustion of two liquids (hydrazine fuel and nitrogen tetroxide oxidizer).
RCS thrusters are mono-propellant thrusters, i.e. they generate gas by decomposing hydrazine on a catalyst bead. Think of your car's catalyser: that is a remote relative of this technology.
This is why RCS thrusters need no oxidizer.

Edit: the OME nominally provides 500 N of thrust, and should now provide about 1/9th of that, i.e. about 55 N.
There are two families of RCS: one providing 23 N and the other 3 N (for roll attitude control only, probably not usable for trajectory control).
I am not sure that using the OME would be a good idea. it would probably use too much hydrazine to provide too little thrust (I don't have info on the fuel consumption of the different thrusters but I assume that that of the OME would be larger than that of the RCS)
Go to the top of the page
 
+Quote Post
Paolo
post Sep 16 2011, 12:39 PM
Post #478


Senior Member
****

Group: Members
Posts: 1729
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



A Mainichi Daily News release: Venus probe unlikely to enter orbit fit for atmospheric observation
Go to the top of the page
 
+Quote Post
Explorer1
post Sep 16 2011, 10:41 PM
Post #479


Senior Member
****

Group: Members
Posts: 2073
Joined: 13-February 10
From: Ontario
Member No.: 5221



Am I right to assume that aerobraking, Magellan style, isn't plausible, if worst comes to worst and the engine is kaput?
Go to the top of the page
 
+Quote Post
Holder of the Tw...
post Sep 16 2011, 11:06 PM
Post #480


Member
***

Group: Members
Posts: 540
Joined: 17-November 05
From: Oklahoma
Member No.: 557



Magellan was already in orbit, and very gradually lowered that orbit a bit at a time with atmospheric friction that was within tolerable limits. To bleed off enough speed all at once to make orbital insertion at the rate Akasuki is going - no, you would be fried. BUT ... if you could manage to get into an orbit with the thrusters, then I don't know, you might look into using aerobraking to get into a lower and more favorable orbit.
Go to the top of the page
 
+Quote Post

50 Pages V  « < 30 31 32 33 34 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th March 2024 - 08:00 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.