The Great Kersten Blunder Blunder

Vigor Venus space probe illustration Per ardua ad nihil.

ISAS/JAXA, Shutterstock/berkut, Phil Plait

I received an email recently from BA reader Derek Armentrout, asking about a story he heard. This anecdote, called “The Great Kersten Blunder”, alleges that a programmer named Kersten made a metric to Imperial unit conversion error that doomed Vigor, a space probe to Venus. Was this legit?

I hadn’t heard this one, so I looked it up. What I found was interesting: If you search on “Kersten blunder” or “Vigor Venus probe” you get the same story, repeated over and again with at most minor changes. Here’s the usual story in its entirety:

The great Kersten Blunder is about the error made by Kersten (programmer) on the Vigor space probe’s converting program. He made an error in the value of converting millimeters to inches. He mistakenly set the value to 24.5 instead of 25.4 which made the probe miss the planet Venus and was consequently lost in space. This Blunder cost the government over 2 billion dollars’ worth of lost technology due to a simple measurement error.

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Great story, right? But a great number of things set off my skeptic alarm:

  • There’s no link to the Vigor Venus probe, or what its mission was.
  • There’s no first name for Kersten, or a link to who he is.
  • There’s no mention of what country launched this probe, or when.
  • There’s no link to any source for this information, no follow-up information, nothing. This is the entire story, soup to nuts.

But I have to admit, the very first thing that made me doubt this tale’s validity was that I had never heard of the Vigor Venus probe, and I’m kinda familiar with space exploration.

Phil PlaitPhil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Now, there are a lot of space missions that have been launched in the past few decades, and it’s pretty hard to keep up with them. A few dozen have been sent to Venus, and I’m not intimately familiar with all of them. Still, I’d’ve at least heard the name before.

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But I prefer to be thorough. I checked, and sure enough, no such mission ever existed. Right away, that’s enough to tell you this story is made up. The other problems I listed are icing on the cake. Searching on a programmer named Kersten just yields this story, or links to people who have nothing to do with space mission planning.

So what gives?

Clearly, someone made up this story. There’s a tiny sliver of truth in it, in that similar errors have indeed been made, resulting in the loss of a mission probe. In fact, NASA’s Mars Climate Observer was lost for just such a reason; Lockheed Martin, a contractor on the mission, had a piece of code that calculated thruster firings in Imperial units, while NASA expected the results to be in metric (specifically SI). This resulted in the spacecraft using the wrong thrust when it attempted to enter Mars orbit. It got too low in the atmosphere and broke apart.

Also, the Japanese Akatsuki mission to Venus did in fact miss the planet, in a sense. A main engine failure prevented the spacecraft from entering orbit around Venus. It continued to orbit the Sun, but engineers were able to use low-power attitude thrusters to put it into orbit around Venus successfully, where it is now operating quite well.

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Perhaps the Mars Climate Observer and Akatsuki stories got conflated and embellished, creating the Kersten Blunder story. Or maybe someone made it up out of thin air (if you pardon the expression). Either way, it was made up.

Still, it’s weird that there doesn’t seem to be any source to this story. I asked some friends who are familiar with space missions past and present, including Jonathan McDowell, Amy Shira Teitel, Anatoly Zak (who knows Russian/Soviet missions) and Bobak Ferdowsi, and none of them had even heard the story (I hadn’t either until I get the email from Armentrout).

Not a single site that talks about it sources the origin, they just repeat it. Answers.com comes up high on search results, and not only treats the story seriously, but gives this clearly inappropriate answer:

What planet did the vigor space probe crash in to?

As far as we know, Vigor hasn’t crashed into any planet.

It was intended to go to Venus, but due to a “small” programming error, it missed Venus entirely and “wandered off into space – AWOL. No one knows where it is now.

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Remember, the Vigor probe never existed! Yet the way the question is answered makes it seems as if it did and that the story is real. Amazing. I’ll add that I find answers.com to be just awful; many, many times I have gone there and seen blatantly incorrect or non-useful answers. Reinforcing this Kersten Blunder story is just more evidence of that. If you’re looking for answers online, I suggest staying away from that ironically named site.

I was surprised to see the story in a UK’s National Physical Laboratory beginner’s guide to mechanical engineering (see page 8). I sent a note to them, and they told me they had noticed the error and are updating the guide, so that’s good.

Also in the good news department: The Straight Dope Message Board has a thread on this topic (Armentrout actually is a member there, which is apparently where he heard the story) with more information. For example, the Mariner 1 probe to Venus was lost five minutes into the flight when a hardware and software failure conspired to doom the mission. This too may have played into this, but I suspect the true origin story may be forever shrouded in internet obscurity.

But there’s a bigger story here, and a very, very important one: Don’t trust anything you hear on the internet. Or anywhere. Ever. Just because someone says something doesn’t make it true.

Ask for evidence. Sources. Supplementary data. And don’t forget to critically evaluate that evidence! If it came from NASA it’s more likely to be factual than if it came from a person you heard on a late night radio show who sells perpetual motion machines and shady conspiracy theories.

The good news here is that this Kersten Blunder story never went viral, and seems to be pretty low-key (it doesn’t feature Mars being as big as the Moon, or a government weather-control conspiracy or a breathless doomsday prediction, so whoever invented it really needs to up their game). But it serves as an excellent cautionary tale to check your sources and never simply accept something just because you heard it somewhere.



from Department of Space Exploration