Wednesday, 20 March 2019

No, the failed Venus lander from Kosmos 482 is not about to come down yet


Venera landing craft (photo: NASA)


Late February 2019, a number of news outlets (e.g. here and here) copied a story that originally appeared on Space.com, titled: "Failed 1970s Venus Probe Could Crash to Earth This Year".

It concerned an unusual object launched 47 years ago, called the Kosmos 482 Descent Craft (1972-023E, CSpOC nr 6073). Word was that it was about to reenter into the atmosphere, maybe even this year.  But will it?  Short answer: almost certainly not.

The source of the prediction is attributed to Thomas Dorman in the Space.com article, but how the prediction was done is not clear from the news coverage. On the request of David Dickinson, who was preparing an article on the topic for Universe Today, I made my own assessment of the issue. I looked at the orbital decay of 1972-023E since 1973 and did some GMAT modelling to gain insight into how the orbital decay will develop in the future.

As I will show in this post, my modelling suggests the Kosmos 482 Descent Craft is not to come down yet for several years.


Kosmos 482, a failed Venera mission


During the 1960-ies and '70-ies, the Soviet Union launched a number of Venera space probes destined for the planet Venus. Some of these probes did reach Venus and even briefly took pictures before succumbing to the very hostile atmospheric environment on this planet. But not all of the probes reached Venus. Several attempts went awry.

Kosmos 482, a probe similar to and launched only a few days after the Venera 8 probe, was launched from Baikonur on 31 March 1972. Reaching a highly elliptic parking orbit around Earth, its apogee kick motor failed to put it into an heliocentric orbit. The space probe broke up into at least four pieces that remained in Low Earth Orbit. Two of these, parts of the rocket engine, reentered within weeks of the failure. Another piece, presumably the main space probe bus, reentered in 1981.

A fourth piece, 1972-023E, is left on orbit, and it is interesting, as it most likely concerns the Descent Craft, the lander module in its protective cover that was to land on Venus, similar to the Venera lander module imaged in the photograph in the top of this post. That makes this a highly interesting object, as it will likely survive reentry into the atmosphere (it was designed to survive reentry into Venus' atmosphere after all).


Orbital decay 1973-2019


Initially stuck in a highly elliptic ~9600 x 220 km, 52.25 degree inclined orbit 47 years ago, its orbit has since decayed considerably. Currently (March 2019) it is in a ~2400 x 202 km, 52.05 degree inclined orbit:

click to enlarge

The diagram below shows how the apogee and perigee changed between January 1973 and March 2019. The orbit has become markedly less eccentric. Orbital decay strongly acted on the apogee altitude. The apogee altitude (blue line in the diagram) has come down steadily and by a large amount, from ~9600 km to 2397 km.This lowering of the apogee is to continue over the coming years. By contrast, the perigee altitude (red line) has changed only minimally, from 210 to 202 km over the past 46 years.


click diagram to enlarge

The apogee altitude will continue to come down. Once it is below ~1000 km, in combination with the low perigee at ~200 km. decay will go progressively fast.


Modelling future orbital decay


To gain insight into the validity of the claim that object 1972-023E might reenter this year, I modelled the future decay of the orbit using General Mission Analysis Tool (GMAT) software. Modelling was done for a 495 kg semi-spherical lander module 1 meter in size, using the MSISE90 model atmosphere.

The result suggests that the Kosmos 482 Descent Craft still has at least 5 to 7 years left on orbit. My model has it nominally reenter late 2025. Taking into account the uncertainties, a reentry between late 2024 and late 2026 seems most likely. That is still several years away.

click diagram to enlarge
click diagram to enlarge

The model result fits well with the trend in the actual tracking data, which gives confidence in the results (the thick lines in the diagrams above are actual tracking data, the thinner lines the GMAT modelled future orbital decay. The latter extend the previous trend in the tracking data well, there are no clear pattern breaks).

It should be well noted that modelling the decay of highly elliptic orbits with high apogee and low perigee is notoriously difficult. Yet, both the past and current orbital parameters and my modelling forecast do lead me to think a reentry is not imminent.

I am not the only one casting some doubt on a reentry of 1972-023E this year. Both NBCnews and Newsweek quote earlier results by Pavel Shubin that predict reentry around 2025-2026, quite similar to my results. They also quote well-known and respected space analyst Jonathan McDowell who is similarly opting for a reentry several years into the future, rather than the coming year.


Conclusions 


From my look at the current orbital decay rate and my modelling of future orbital decay, supported by assessments from other sources, it appears that the newsreports suggesting that the reentry of the Kosmos 482 descent craft is imminent and might even occur this year, are in error.

As to the why of the discrepancy: in the Space.com article, Dorman is quoted claiming "Our guess is maybe as much as 40 to 50 percent of the upper spacecraft bus may still be there". It is not clear at all what this "guess" is based on. My own modelling shows that the mass and size of the landing module only (i.e. without other parts still attached), fits the current orbital decay rather well. It is not clear how Thomas reached his conclusion, but modelling with a wrong mass and/or size might explain the discrepancy between my result and that claimed in the Space.com article.

I am hesitant with regard to accepting the high resolution imaging attempts by Ralph Vandebergh featuring in the Space.com article as evidence for object 1972-023E being more than the lander module only, as the weak and rather irregular protrusions visible might be image artefacts from atmospheric unrest and camera shake rather than real structure. Even when telescopically imaged at minimal range in perigee, we are talking about apparent object sizes at the arcsecond level and single pixel level here, conditions under which it is very challenging to image detail. Under such challenging conditions, spurious image artefacts are easily introduced.

Acknowledgement: I thank David Dickinson for encouraging me to probe this issue.

3 comments:

Lysergic said...

Super interesting, always enjoy your posts Marco.

Thomas Dorman said...

Marco
First a lot was left out of story posted on Space.com. Second you may have missed that there was a second prediction from a unidentified source in the article giving a decay in 2.5 years. If you do some research there is also a prediction that puts the decay of Cosmos 482 out as far as 2035.
Next Marco have been observing and studying Cosmos 482 for more than 20 years as to the remains and a new study of images points to the fact that more of the spacecraft remains than just the sphere. Then also what was left out of the story is in 2018 we sent a proposal to the TARA radar staff to see if they would image the spacecraft when it comes to the suitable altitude for their system to help settle this question. They agreed to make such observation. Yep, Marco we are will to be proven wrong in our prediction on how much of the spacecraft remains and have helped advocate to be proven wrong!
As for our prediction we did not speak in absolutes as you have to when Cosmos 482 would decay we openly stated it was a "guess" and made it more than clear to Mr.David it was a "guess".
Believe others and you are reading more into the article than is there for whatever reason!
Last if you are honest you would admit that predicting an accurate satellite decay ,especially with an orbit such as Cosmos 482, is more an art than science and a flawed art at that as your own prediction shows with a reentry window error of two years.

Unknown said...

Marco,
If you read my observational webpage about Cosmos 482, you should have seen that I don't claim anything myself about the high resolution attempts. I just report that the object appears mostly elongated and has brightness variations.

http://www.ralfvandebergh-astrophotography.simpsite.nl/lost-planetary-spacecraft

Ralf