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#420 by kevin-rf on 23 Nov, 2011 22:16
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Thank you, ESA and Perth! However...is there some reason this wasn't tried sooner? Was the orbit not right for contact from Perth, or is that Russia only finally asked?
Maybe it was not configured correctly and time had to be spent setting it up. They did make some antenna mods to pull this off. -
#421 by Kaputnik on 23 Nov, 2011 22:26
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Can they adjust P-G's tragectory to be more inline with MSL? Could they spend some of that extra fuel to get it back on course? Too bad it can't berth with MSL and hitch a ride!
This is discussed a couple of pages back. MSL is on a direct entry trajectory so can afford to arrive a bit faster. If PG flew the same trajectory it wouldn't have enough propellant to brake into orbit. -
#422 by PeterAlt on 23 Nov, 2011 22:33
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Thanks. I just read that page. I like that Deimos idea that was suggested. No one answered if it is possible....
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#423 by Chris Bergin on 23 Nov, 2011 22:33
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BBC's Jonathan Amos wrote "Phobos-Grunt still has a short window in which to start its journey before a change in the alignment of the planets makes the distance to the Red Planet too big to cross."
Is he wrong? -
#424 by Skylab on 23 Nov, 2011 22:41
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BBC's Jonathan Amos wrote "Phobos-Grunt still has a short window in which to start its journey before a change in the alignment of the planets makes the distance to the Red Planet too big to cross."
That seems to be a possibility when you move the planning of the sample return to the right. So, launch now, sample return in 2016. Someone please correct me if I'm wrong there.
Is he wrong? -
#425 by hop on 23 Nov, 2011 22:45
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BBC's Jonathan Amos wrote "Phobos-Grunt still has a short window in which to start its journey before a change in the alignment of the planets makes the distance to the Red Planet too big to cross."
Like everything else about this mission, there's a lot of contradictory statements floating around, including "official" statements. IIRC Popovkin said they could still make it in early December. Others suggested that orbital precession ruled out a successful mission long before the end of the nominal window.
Is he wrong?
David Warmflash (PI for the LIFE experiment) suggests that the return trajectory dictated the window http://www.universetoday.com/91239/contact-established-with-phobos-grunt-spacecraft-can-the-mission-go-on/ This seems odd, given the duration of the nominal Phobos stay, but I doubt he's just making it up. Maybe there's knock-on effects on how long it takes to match Phobos orbit (pure speculation on my part) ?
Clearly, the Russians picked their nominal window for a reason. It's also safe to assume that nominal window preserved some margin, so stretching it may be possible.
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#426 by Nickolai on 23 Nov, 2011 22:46
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Not to stifle discussions of alternative missions, but let's all keep in mind that the health of the spacecraft has not been fully ascertained. It's quite possible the main engine is not working, so any potential trip to Mars or Phobos or Deimos or wherever would be out of the question.
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#427 by iamlucky13 on 23 Nov, 2011 22:48
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Can someone elaborate on this answer? Jim's post is no more meaningful to me than if he had said "Number 1 vs Number 2 trajectories."
First hit on Google with "mars type 1 2 trajectories":
http://www2.jpl.nasa.gov/basics/bsf4-1.php
The two short sentences about it on that page are only minimally enlightening, although I have found a little more, including some discussion in the context of Venus windows here:
http://www.mentallandscape.com/V_VenusMissions.htm
From a practical standpoint, I gather the two trajectory types arise because there isn't actually a single ideal Hohman transfer orbit for multibody systems with varying inclinations. If you look at a porkchop plot (basically a graph of the characteristic energy (C3) required to make a transfer, graphed as launch date versus arrival date, with C3 shown by contour lines, colors, or a third dimension) you see two zones of minimal transfer energy. These aren't necessarily equal, but they do define two distinct opportunities.
Wikipedia has a more relevant plot from the 2005 window used by Mars Reconnaissance Orbiter
http://en.wikipedia.org/wiki/Porkchop_plot
Blue contours are characteristic energy. Red lines are transfer times.
The minima on the lower left is the type 1 trajectory. If you view it full size so you can see the numbers, you will notice it is faster, but takes a hair more energy.
A related question I haven't found an answer to yet is if it is always the case that type 2 is more efficient?
Time is an obvious a reason to choose a type 1 trajectory (idle science teams cost money, hardware ages and experiences cosmic ray exposure, radioactive isotopes decay, etc). However, you also sacrifice mass, so I'm led to wonder if, for example, orbital missions may tend to more greatly benefit from a type 2 trajectory than direct entry missions.
* Edited - fixed first link -
#428 by Skylab on 23 Nov, 2011 22:48
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As mentioned here: http://www.universetoday.com/91239/contact-established-with-phobos-grunt-spacecraft-can-the-mission-go-on/
(Ah, Hop beat me to it.
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And here: http://www.universetoday.com/91207/can-phobos-grunt-still-be-saved-scientists-hold-out-hope-as-deadlines-loom/ -
#429 by rnc on 23 Nov, 2011 22:58
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Thank you, ESA and Perth! However...is there some reason this wasn't tried sooner? Was the orbit not right for contact from Perth, or is that Russia only finally asked?
Maybe it was not configured correctly and time had to be spent setting it up. They did make some antenna mods to pull this off.
From the ESA article, they have been trying since 9th Nov. They have installed (and aligned) an antenna on the dish, plus electronics, plus heaven knows what to achieve this. Significant effort. -
#430 by Chris Bergin on 23 Nov, 2011 22:59
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Yikes, that Universe Today article's a bit good! Mine - which is complete, but just finding pictures etc - is going to be bare bones, just to allow something to be used as "developing news".
I would note I was writing a very good SLS article before all of this
#ChrisPrefersNASAVehicles -
#431 by Skylab on 23 Nov, 2011 23:00
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Quote
Repeated contact with the spacecraft "Phobos-Grunt" was a success. As reported by a correspondent. ITAR-TASS in the NGO SA Lavochkin, with an automatic interplanetary station radio signal was received back.
Source: http://www.itar-tass.com/c19/280016.html
The current attempt to become the second after the night from Tuesday to Wednesday ground stations Perth / Australia / able to get a first response signal from the "Phobos-Grunt" after its descent from orbit. As explained in the European Space Agency / ESA / now its specialists sent new commands that are "allowed to obtain telemetry data."
Could someone check that automatic translation? -
#432 by Chris Bergin on 23 Nov, 2011 23:04
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And would it be fair to say the first successful attempt Tuesday evening GMT was commands to the spacecraft. However, the telementy was on a latter pass, not the first one? (There's conflicting reports on that too).
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#433 by Skylab on 23 Nov, 2011 23:08
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And would it be fair to say the first successful attempt Tuesday evening GMT was commands to the spacecraft. However, the telementy was on a latter pass, not the first one? (There's conflicting reports on that too).
From what I've read, the first one only got the carrier wave/signal, while the second contained abbreviated telemetry data. -
#434 by asdert on 23 Nov, 2011 23:10
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BBC's Jonathan Amos wrote "Phobos-Grunt still has a short window in which to start its journey before a change in the alignment of the planets makes the distance to the Red Planet too big to cross."
Is he wrong?
The expression that the distance will be "too big to cross" is maybe not very accurate. In fact the longer trajectories cost less engery (with the Hohmann transfer as extreme). For shorter routes you need more delta-v, so more fuel, but less time. It is not the distance that makes it easy or hard, it is the delta-v, which translates into fuel.
The later Fobos-Grunt is sent to Mars (with a proper TMI here), the more fuel is reqiured. The more fuel is spent during the TMI, the less is available for the rest of its job. -
#435 by Chris Bergin on 23 Nov, 2011 23:12
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And would it be fair to say the first successful attempt Tuesday evening GMT was commands to the spacecraft. However, the telementy was on a latter pass, not the first one? (There's conflicting reports on that too).
From what I've read, the first one only got the carrier wave/signal, while the second contained abbreviated telemetry data.
Thanks! That's how I've read it on the updates here, but wanted to double check
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#436 by pm1823 on 23 Nov, 2011 23:12
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Could someone check that automatic translation?
Ignore it. Bad written old news. -
#437 by hop on 23 Nov, 2011 23:21
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Matches Anatoly Zaks account here http://www.russianspaceweb.com/phobos_grunt_launch.html#11_23And would it be fair to say the first successful attempt Tuesday evening GMT was commands to the spacecraft. However, the telementy was on a latter pass, not the first one? (There's conflicting reports on that too).
From what I've read, the first one only got the carrier wave/signal, while the second contained abbreviated telemetry data.
The ESA page currently only confirms the first contact: http://www.esa.int/esaCP/SEM4NEZW5VG_index_0.html
The statement from ESAs Rene Pishel saying they have telemetry is quoted here (in Russian): http://ria.ru/science/20111124/496387514.html
edit: English version http://en.rian.ru/science/20111124/168984266.html -
#438 by pm1823 on 23 Nov, 2011 23:27
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RIAN is good source, they use naming and quoting of their sources.
Mr. Zak often using NK forum. ESA is original source on this info.
Interfax - too late, too many errors and very small understanding. -
#439 by Prober on 23 Nov, 2011 23:32
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Thank you, ESA and Perth! However...is there some reason this wasn't tried sooner? Was the orbit not right for contact from Perth, or is that Russia only finally asked?
Maybe it was not configured correctly and time had to be spent setting it up. They did make some antenna mods to pull this off.
From the ESA article, they have been trying since 9th Nov. They have installed (and aligned) an antenna on the dish, plus electronics, plus heaven knows what to achieve this. Significant effort.
the AP says that they tricked(my words) the Antenna with a very low signal, like FG is far away from earth.
)