# “UK schoolboy corrects Nasa data error” - what precisely was the “error”?

A British schoolboy has discovered that a piece of Nasa's top space research is flawed.

Miles Soloman, a student at Tapton School in Sheffield, was taking part in a project run by the Institute for Research in Schools. He told the World At One how he discovered that equipment used by the International Space Station was recording false data. (emphasis added)

A further BBC article and interview can be found here. From that article:

During UK astronaut Tim Peake's stay on the station, detectors began recording the radiation levels on the ISS.

"I went straight to the bottom of the list and I went for the lowest bits of energy there were," Miles explained. Miles's teacher and head of physics, James O'Neill, said: "We were all discussing the data but he just suddenly perked up in one of the sessions and went 'why does it say there's -1 energy here?'"

What Miles had noticed was that when nothing hit the detector, a negative reading was being recorded. But you cannot get negative energy. So Miles and Mr O'Neill contacted Nasa. "It's pretty cool", Miles said. "You can tell your friends, I just emailed Nasa and they're looking at the graphs that I've made."

It turned out that Miles had noticed something no-one else had - including the Nasa experts. Nasa said it was aware of the error, but believed it was only happening once or twice a year. Miles had found it was actually happening multiple times a day.

Prof Larry Pinksy, from the University of Houston, told Radio 4: "My colleagues at Nasa thought they had cleaned that up.

Precisely what NASA top space research "is flawed" because it is recording "false data"? What data stream are we talking about, and is the problem catastrophic, or just LSB noise (least significant bit).

• It was basically how a U.K. student found out radiation level of ISS suddenly perks and other times remain at value of -1. Yet it did not specify the units of radiation and the article was poorly written, it would be an better idea just to e-mail NASA about the data. – Raze Mar 26 '17 at 8:33
• @Raze I'm not asking you to read the article I've linked to and tell me what it says. People familliar with NASA (and some who work at NASA) read questions here and leave helpful, authoritative answers from time to time. Have some faith in stackexchange! :) – uhoh Mar 26 '17 at 8:38
• A common practice in data formats for scientific instruments is to use -1 as a "missing value". The value is missing either because something prevented a measurement from being taken (such as the position of the satellite) or the instrument itself returning an error condition or a not ready condition. This can happen, for example, if the instrument is resetting itself, doing a self-check, or for other reasons. – Tyler Durden Mar 26 '17 at 14:01
• “UK schoolboy corrects Nasa data error” is better clickbait than “UK schoolboy notices minor data anomalies” – barbecue Mar 26 '17 at 16:01
• @uhoh Understood, I was just making a snarky comment on the ubiquitous use of clickbait headlines by even respectable news organizations. – barbecue Mar 27 '17 at 1:02

The source of the data is the Radiation Environment Monitor. Lawrence S. Pinsky is listed as co-investigator.

This Radiation Environment Monitor demonstration will provide information that is required to enable the design of an operational active personal space radiation dosimeter.

The objectives of the experiment are to demonstrate the viability of this technology in the space radiation environment and the ability to assess crew exposure in near real time (via ground software).

In order to effectively manage radiation risks to crewmembers during long-duration space exploration beyond low Earth orbit, there is a strong need to monitor personal radiation exposure in near real time. The current technology uses passive dosimetry techniques and associated logistics that require down-mass and ground analysis which provides radiation dose information several months after return. The REM is a low mass, low volume and low power dosimeter that may meet the near real time exposure monitoring of crew members.

The REM devices are USB sticks.

The error was a misunderstanding of the root cause of the negative values:

NASA had apparently already known about this issue, but they thought it was only occurring once or twice a year due to a problem with an algorithm. But Soloman found it was occurring multiple times a day.

Why the REM records negative values remains to be seen.
But it is not unusual to use 'impossible values' to convey information, where -1 could mean 'measurement out of range'. There's a name for this phenomenon, but that escapes me at the moment.

If you misread the -1 as a literal value, its impact depends on the rest of the data. If the data has a range of 0-10000, the impact of having a few instances of -1 that should be 0 is small. If the values are in the range of 0-10, its impact is much larger.

• Thanks for the thorough answer. A low mass dosimeter, read out frequently, might read an occasional zero, and if there is any offset at all, calibration or otherwise, occasional negative numbers are possible, and of course the -1 being a flag is certainly reasonable too. I can't read the article yet, but in the preview of the figures I see a map of the ISS orbit and variations in dose resolved within a single orbit. Typically personal dosimeters are read out daily, or even once a week, and other types of radiation monitors are used for spatial or temporal mapping and/or safety alarms. – uhoh Mar 26 '17 at 11:40
• I'm going to conclude personally that the BBC's choice of words "...a piece of Nasa's top space research is flawed." are overstating the situation somewhat, actually more than somewhat. – uhoh Mar 26 '17 at 11:42
• Note that the impact does not only depend on the range of usually expected values. If you only ever expected non negative values and suddenly get a -1 then this can screw calculations (if not guarded correctly) pretty much (think what happens to log .. ) – Daniel Jour Mar 26 '17 at 13:36
• "There's a name for this phenomenon", sentinel values. – longneck Mar 26 '17 at 13:48
• Magic number – Steve Mar 28 '17 at 19:08