Well, the Mars-2 and Mars-3 landers are separate cases. Mars-2 was planned using innacurate data about the atmosphere, leading to a suicide trajectory. The only way we will ever know what happened to Mars-3 is the very remote chance that something is recovered off the transmission tapes or the more likely chance that orbital imaging picks it up and gives clues to what might have happened. In the case of Mars-3, the Soviet scientists did try to process the tapes to pull out a signal beyond the time of loss of contact (this worked for Venera-7), but with no luck. I still would love to give modern equipment a crack at it. They indeed had a simpler landing technique. Also, the Vikings are the only planetary landers to have been placed into orbit until an opportune time, after the sites had been surveyed and atmospheric conditions were checked out. A very interesting thing is the Mars'96 penatrator design, which takes the hard lander idea to a new level. The MetNet landers are basically Mars-96 penetrators with improved instruments, so that design isn't dead. The small station design was never built on, but a major reason for that is the fact that the MetNet hard landers can do almost everything that the small stations were going to do and are cheaper, so thanks to improved instrumentation, they are no longer needed.

Yeah, MetNet is an elegant decision. However, I'd like to see them traveling aboard Phobos-Grunt rather than launching them separately with a Volna rocket (which will be suicidal for the mission).

Why is that suicidal? The Phobos-Grunt plan was to release the Metnet lander(s?) before entering orbit, so I don't see a difference. The only thing I wish is that they were sending more than one. A badly placed rock could ruin the mission.

I personally see Volna as an unreliable vehicle.

Oh, OK, in the sense of possible launch failure. I see what you mean now.

Yeah, that's what I meant. Volna failed to launch Cosmos 1 twice. Also we will need a new stage for an interplanetary flight + a cruise stage that has yet to be developed. If MetNet is aboard Phobos-Grunt it won't need it.

My guess is that the little Chinese orbiter took its place on Phobos-Grunt. I would imagine that funding is a major issue. The very existence of the mission owes itself to a way Russia could pay back debt owed to Finland in the late 1990s. At the time, Russia was hat-in-hand, but things have changed, and they may not want to sink more into the mission, given that they could easily afford to just pay Finland now.

I understand, but I also don't see how the design of both Metnet and Yinghuo fits in the overall mission. The oldest schemes I posess are from laspace.ru and they are in Russian (no problem for me, I can read it). How are they going to attach the orbiter? Will it be power-independent during the cruise phase? Will it use its own engines for MOI or it will relay on the engines of Phobos-Grunt?

I have those diagrams and have wondered the same thing. My only guess is that it will be released before MOI. Given the huge elliptical orbit Yinghuo is supposed to have, it will probably do its own MOI. I have no idea about power during the cruise phase.

You are probably right. The Chinese orbiter will be dedicated mainly to studying the upper atmosphere and the interplanetary medium. It doesn't need to be into a low Martian orbit.
As for Phobos-Grunt I have also some worries. It's more complicated mission that Phobos 1/2 and Soyuz doesn't have the capability of Proton. Does that mean that a most of its systems aboard have no redundancy?

I think a lot of it has to do with the fact that in the post-Soviet era, miniaturization has greatly improved. I still worry. While NASA has a nasty habit of launching missions stripped down to just a few instruments, Russia has a real problem with trying to load every imaginable device onto a probe creating very high levels of complexity (and many opportunities for failure).

Yeah, that's why the failure of Mars 96 was really bad. Some of the instruments (HRSC, OMEGA) were reflown aboard Mars Express, others ... well, that's the real loss.

One of the instruments was developed (at least partially) in Bulgaria. It's RADIUS-M. It was supposed to study radiation and if I recall correctly, it's the last Bulgarian scientific instrument which flew aboard an interplanetary mission. I'm sure that another radiation instrument, developed by IKI-BAN will fly aboard Chandrayaan and I hear unofficial rumors that Bulgarian scientists are working with Russian scientists on Phobos-Grunt. Does that mean that they are going to fly once again another radiation dosimeter? I still don't know.

Oh well, here is a link:

http://www.bnr.bg/RadioBulgaria/Emission_E...erial/April.htm - it says a little, but briefly that a "gauging instrument" will land on Phobos. So, yes, they may refly RADIUS-M.

I hope it makes it on there!

By the way, here is a link to the page in Harvey's book where he makes his claim.

http://books.google.com/books?id=jKmIclMIw...p8C54&hl=en

Ted, I'm reading the upper link with a great interest. About Mars 6: it says that the photometer took colour filter images of the atmosphere. Do you have some images (as files)? I had once, on a paper and I lost it

I don't think the Mars-6 flyby module took images. The Mars-4 and Mars-5 craft took pictures with a photometer. Mars-6 had one, but I don't think it was used (I could be wrong). Given Harvey's story about the Mars-3 "image," his book is not a credible source. Here are the Mars 4 and 5 photometer images.

http://www.strykfoto.org/mars4and5.htm

The Mars-6 lander carried a photometer which was used to measure lightlevels, probably similar to instruments carried on the Venera Venus landers.
Quote: "Contrary to exaggerated press reports, it seems unlikely the instrument was able to return color images" (ref. "Mars 5 and 6 Flight Analysed", Flight International, 4 April 1974 439-440, also ref "Robotic Exploration of the Solar System" Ulivi/Harland, page 167).

I have never seen any reference to pictures taken by the flyby bus of Mars 6 or 7, only pictures taken by Mars 4 and 5 have been published.

I would almost wonder if that reference is to Mars-4 and 5. None of them had color photometers, but instead operated at visible and infrared wavelenths. The film cameras could take color pictures, and Mars-5 returned a few before it failed. Pverkhnosti Marsa is the best reference with regard to this mission.

A different story on Mars 2 and Mars 3.

Where did they land and why were those places chosen? I was just plotting the locations on maps of image coverage from previous missions. Mars 2 crashed in Hellas, in the area imaged by Mariner 7. Mars 3 landed right on the southwest corner of Mariner 4 image 13, south of Newton crater. This suggests its target was actually inside the imaged area. The target latitude would be defined by EDL design and the seasons on Mars, and is about 45 south for both missions (incidentally, Wackypedia is waaay off with Mars 2... where did that come from?). It makes a lot of sense for the two mission targets to be in the only areas imaged at that time at that latitude. The site's geological context would be known. And Mariner 7 images seemed to show Hellas was a very smooth plain (actually it was looking at clouds inside the basin), so it would be safe.

So all that looks like it might make sense. But then this can potentially be used to resolve the discrepancy in longitudes between NSSDC and Astronautix.com site locations. Astronautix longitudes are ten degrees larger than NSSDC longitudes. But the Mars 3 site wouldn't be in the image area if the larger longitude value is used.

EDIT - next day - oops, I'm maligning Astronautix, the incorrect location actually came from http://history.nasa.gov/SP-4212/ch9.html (The NASA history volume on Viking). (Possibly the website used that value earlier and has edited it recently)

Any thoughts?

Phil

According to Sasha Basilevsky, Hellas was chosen for exactly the reasons you say (based on a conversation I had with him). As far as Mars-3 goes, I have no clue.

Yikes - Google Mars has Mars 2 at the stupid Wikipedia location - it's a travesty ah tells ye!

Phil

How much certainty do we have on the Mars 2 position. According to most accounts it was released in the wrong orientation (or at least with the wrong coordinates set) after a failure of the mothership to update the lander data. This in turn resulted in a steep dive into the atmosphere and a crash before the parachutes could be deployed. This sounds to me like it went waaay offcourse. Hellas was probably the chosen landingsite for Mars 2, but it might have missed its target by an enormous distance and I doubt if there is much knowledge as to where it eventually crashed...

Given all the uncertainties with ephemeris data at the time and the various coordinate-systems used, I doubt whether any of these probes are anywhere near their stated coordinates.

Way off course by a few hundred km maybe, not half way round the planet.

Phil

I agree on you with that.

I have often wondered how the autonomous navigation prior separation/EDL worked on Mars 2-3. They had quite a big problem due to inaccurate ephemeris data on Mars, that's why they needed an orbiter around Mars prior to both landers, when that launch went wrong they had to rely on the untested autonav function from the landers.

The landers had a solid propellant retro-engine, so their retro-impuls was more or less fixed (they could change the orientation but not the duration of the impuls) and from the various accounts it reads like the whole entry sequence was mostly completely fixed and not much could be changed on the spot (even orientation engines were partly 'gunpowder' engines, so fixed impuls). Entry and landing was a parabolic trajectory. Thus everything relied on the mothership releasing the lander on exactly the correct trajectory and in the correct orientation.

The latitude of 45 degrees south for both landing sites corresponds more or less with the inclination of the final orbits of both motherships, and might thus have been a pre requisite of the automatic entry-sequence.

With uncertain ephemeris, the mothership had to update its own statevector prior to release of the lander (using Mars and Sun?), then calculate its final course correction in order to steer to the correct trajectory. Afterwards the mothership had to place itself in the correct orientation, and release the lander (sounds like lander was spin-stabilized afterwards till firing of its retro engine, and then steered into correct entry-orientation). By the sound of it, this was all done automatically and pre-programmed, quite a feat for 1971 technology. It is unclear whether there were any communications from the lander after release, on Mars 6 it is stated that an extra transmitter was added to transmit data during the parachute descent, and this sounds like Mars 2/3 did not have such a transmitter or maybe only very basic telemetry was send.

The fact that the landingsites were chosen from mariner 6/7 images is very interesting and makes sense as these images were freely available at the time and were the best there was to have, but without accurate ephemeris data and with pre-programmed entry-sequences it sounds landing accuracy must have been very low, which makes finding those probes almost impossible.

Regards,

Geert.

There were not (except for the short signal from Mars-3's decent craft after reaching the surface). After the Mars 2/3 experience, they the transmitter used during descent to Mars 6/7. Sadly, the U.S. would learn the same bitter lesson with MPL.

'The fact that the landingsites were chosen from mariner 6/7 images is very interesting and makes sense as these images were freely available at the time and were the best there was to have'


Before the landing an airbrush map was prepared by the USGS for the Russians of the Mars 3 landing site, which as I recall was of the northern Argyre basin. I remember after the landing failure Dick Pike fretting, as if the Survey had somehow shared the blame by leading them to a bad spot!!

Don

Hi Don! You are thinking of Mars 6. The Mariner 9 images were not available to support that kind of mapping for Mars 3! Mars 6 landed just north of Argyre and a USGS map of Nereidum Montes was indeed published at that time, and used in a Russian paper on the mission, published in Cosmic Research.

Phil

http://www.laspace.ru/rus/mars23.php

Lavochkin website on Mars 2 and mars 3. Hmmm. This is the source of the Wikipedia location for Mars 2 - 4° north, 47° west, near Nanedi Vallis in Xanthe Terra. (Thanks Maxim for the information).

But this is completely at odds with information published at the time (links I'll have to dig out, but I think Marov & coauthor, Icarus, 1973) (atmospheric entry at 45 south, 313 west, with crash near 45 south 302 west).

I'm not sure where this leaves the problem, but I don't think it is likely that these coordinates can be correct.

Phil

I fully agree with you that they are very (unlikely) far from the planned landing at Hellas.

Perminov ('The difficult road to mars' NP-1999-06-251-HQ) does not mention any crash-location for Mars-2, and in my opinion his booklet is a quite accurate source for Soviet planetary flights in that period. If he does not mention a crash-location it sounds like nobody at the time was quite sure as to where it ended. If there were indeed no communications with the Mars 2/3 landers after release of the orbiter until after landing then how can we be sure its retro rocket actually fired? The lander might have missed Mars completely and ended up in solar orbit...

I'm still trying to work it out, but the landers used a solid propellant retro rocket, causing a 120 m/sec velocity change. They were released at 46000 km from Mars in an orientation almost perpendicular to the fightpath (drawing at page 53 of the Perminov booklet). The lander was spin-stabilised after release and automatically fired its rocket 900 seconds after release, everything completely pre-programmed. As it was released perpendicular to the flightpath, the pulse of the lander engine did not so much 'brake' its speed as well change the vector and reduce the fly-by distance from 1500 km to zero. In this scenario there is actually not so much you can do to 'steepen' the descent, almost any error in orientation will cause the lander to 'miss' Mars altogether and disappear into solar orbit.

So, it sounds like the whole scenario depended on the trajectory of the mothership at the moment of release, and this is probably what went wrong with Mars 2. According to plan (Perminov, page 53 again) the mothership would be in a trajectory with a fly-by distance of 2350 km +- 1000 km prior to its third and final course correction. This course correction was automatically computed by the onboard computer, and should have resulted in a fly-by distance of 1500 km +- 200 km, where after the lander was released. On Mars 2 the mothership was actually in a fly-by trajectory with a fly by distance of aprox 1500 km prior to the third correction, but instead of skipping the third correction, the onboard computer ordered a third correction which actually 'overcompensated' and decreased the fly-by distance too far. (Perminov, page 57). Mars 2 there after ended up in an orbit with a perigee of 1350 km instead of 1500 km.

Thus it sounds like the whole error was in the final trajectory on release of the lander, which was too steep with a too close fly-by distance. Supposing the lander rocket fired correctly (which we can't be sure of!) this would indeed result in a descent which was too steep.

However, the trajectory can't have been too far off, otherwise the mothership would have burned up in the atmosphere, which it didn't. It's all 'back of the envelope' calculations, but let's say Mars 2 was 300 km 'off track' on release of the lander, then the final entry trajectory of the lander must have been 300 km off track as well (impuls of solid rocket was fixed, lander sequence pre-programmed). Given a Mars radius of 3396 km, this would result in an atmospheric entry angle of 90 - ASIN((3396 - 300) / 3396) = 25 degrees, which is obviously too steep.
Presuming the original entry angle was close to zero, error in landing location would in this case also be 25 degrees, or 1481 km. (see attached drawing).

Click to view attachment

The very, very, worst case scenario (given the mothership did not burn up in the atmosphere, so must have passed let's say minimum 200 km) would put the lander off track by 1300 km perpendicular to its trajectory, which will give an atmospheric entry angle of 52 degrees and an error in landing location of 3081 km. That's absolutely the very worst case scenario, I can't create a bigger error given the fact that the mothership obviously survived...

So 'most likely' error would be in the range of 1481 km maximum and absolutely worst case error would be 3081 km. It looks to me like the lander was targeted for the Hellas bassin (they seem to have targeted for locations imaged by Mariner 4/6/7 so targeted area must be within one of these pictures), so draw an E-W elips with a maximum radius of 1481 km centered on the Hellas location and start searching...

Note this is all 'back of the envelope' calculating, obviously a lot of factors aren't taken into account but it give's the basic idea of what error we are looking for.

Regarding Mars 3 and 6, the Perminov booklet states a maximum allowed error in atmospheric entry error of 5 degrees, if you ignore all other factors, this gives a landing elips with a maximum radius of almost 300 km (any bigger error and they wouldn't have survived entry). It remains a very big area to search...

Regards,

Geert.

Forgot to mention that according to the above reasoning, the crash location of Mars 2 must be to the WEST of Hellas, as we know it entered too steep. So it must be at least 300 km west of its intended spot (atmospheric entry angle must have been more then 5 degrees too steep, otherwise it would have survived), and it is likely no more then let's say 1500 km to the west (given the final orbit of the mothership) but definitely no more then 3100 km west of Hellas (otherwise the mothership would have burned up). It remains a big, big area...

Click to view attachment

Track projected on Google Mars. If we assume a landing error of 700 km (which correspondents with a most likely offtrack of 150 km, given the mothership entered an orbit with 1350 km perigree instead of 1500 km) then the targeted landing site would be close to 45S 70E which is almost dead centre in Hellas. I am trying to find out whether this area is inside one of the Mariner 7 images.

Anyway, no matter how I try I can't get Mars 2 to end up anywhere near 4 N. This also does not work out with the mothership ending up in an orbit with a 49 degree inclination, given the relatively small impuls of the lander-engine the atmospheric entry point must be close to the groundtrack of the mothership, which is conform with the 45 deg South locations but definitely does not work out for any location on the northerly hemisphere.

Regards,

Geert.

Thank you for this very comprehensive and interesting analysis, Geert.

I'm more convinced than ever that the only way that these landers will ever be found is by somebody tripping over them in the year 2300 or so. We've already seen that very recent meteoritic impacts leave pronounced scars on the Martian landscape, which is a significant contribution to the S/N ratio; given also the large uncertainty in landing locations (to say nothing of circumstances), there's really no assured way to find them from orbital imagery.

Now, since historically every absolute statement I've ever made has been 100% wrong, let's sit back & wait for the break-through.

Okay, one more remark and then I leave you in peace

You quote Marov & coauthor, Icarus, 1973 for Mars 2 atmospheric entry at 45 south, 313 west, with crash near 45 south 302 west.

Now covered distance is 11 degrees longitude, this is (11/57.3 * 3360)COS(45) = 456 km
If we assume atsmopheric entry was at 100 km altitude, with a purely ballistic trajectory and discounting all atmospheric influences (..) then the entry angle must have been ATAN(100/456) = 17 degrees.

Now I remarked the lander was most probably 150 km off track on its trajectory (given the fact that the mothership ended 150 km low on perigree), if you calculate the entry angle from this fact then the entry angle must have been 90 - ASIN((3396-150)/3396) = 17 degrees !!!

Seems almost too good to be true...

The altitude typically used today is 125 km for atmospheric entry. I am not sure what was used in this mission.

I think it might be sooner than that, maybe before the end of the century. Remember how distinctive in colour artificial objects imaged by HiRISE have appeared.
Perhaps some future orbiter using optical communication as standard will be capable of returning multi-spectral imagery with CTX-like coverage and HiRISE-like resolutions.