# Tag Info

## Hot answers tagged unit-systems

82

The Apollo Guidance Computer did use metric/SI units internally for its calculations. But it converted to imperial/USC units when it displayed data on the DSKY. This is probably because the Apollo astronauts (mostly trained as test pilots) had an intuitive "feel" for imperial/USC units. Although data was stored internally in metric units, they were ...

49

NASA formed a board to investigate the loss of the spacecraft and reached some high level conclusions. The board cited a number of contributing factors, which I have filtered to include the ones most relevant to the question: errors went undetected within ground-based computer models of how small thruster firings on the spacecraft were predicted and ...

36

NASA used English Engineering Units not Imperial units. (This phrasing is a reply to the original, un-edited question title) They did this because the program was implemented by the US aerospace industry and that industry's industrial base was all in English units. Every manual, tool, data book, milling machine, and fastener used those units. Conversion ...

26

There were a good number of chances to catch the error after launch, which is what most of the reports on the mission focus on. To look specifically at what testing was done before launch this paper from the American Astronautical Society has a decent overview, starting on page 6: The failures of the Mars Climate Orbiter and Mars Polar Lander: a perspective ...

26

Both, apparently, at least the ones the crew can access. Their toolbox features both systems.

15

Project Mercury used imperial units of measure. For example, the Mercury spacecraft main instrument panel indicated altitude in FT (feet):        The Mercury spacecraft main instrument panel from Project Mercury Indoctrination, May 1959 (Source: NASA. Click for full size) They used statute miles as a measure of distance in ...

10

When I was trained in Aerospace Engineering at Texas A&M in the 1980s, we were taught to use what has been referred to as the Gravitational FPS system, where distance is measured in feet, force in pounds, and mass in slugs. This was a big disappointment to me at the time, since I had been quite comfortable with metric units in high school physics. ...

9

Is it... the gravitational potential energy of one pound hoisted one foot in a constant gravitational field...? Yes indeed it is! To be energy, the pound has to be parallel to the foot. $$E = \int \mathbf{F} \cdot d \mathbf{s}$$ To be torque, the pound has to be perpendicular to the foot $$\tau = \mathbf{r} \times \mathbf{F}$$ 1 foot-pound (or pound ...

8

The entire Lunar Roving Vehicle Operations Handbook (PDF, 38 Mb) is in meters. The only mention of "foot" is when talking about the astronauts' footrests, and "feet" does not appear at all. Kinda unexpected, considering that Boeing was the rover contractor. Section 1.5.6 describes the Speed Indicator: The instrument shows LRV velocity from 0 to 20 km/...

8

The LRV was at least partially metric. But they used a mix of metric and US customary units. Temperatures in Fahrenheit. But when you decide to use km for distances, you have to use km/h for speed. Snippets from this paper.

4

Foot-pound or pound-foot are synonymous, and represent the arithmetic product of pound (force) and foot (length). The pound (force) is the weight of one pound (mass) at the Earth's surface (somewhat imprecise because Earth's gravity field varies depending on your location, and the effective weight of an object will be influenced by the centrifugal force due ...

4

If the decision of NASA from January 8, 2007 to use only metric units for all operations on the lunar surface when it returns to the Moon is still valid, it should be valid for the Orion capsule too. See this page. ISS seems to be not pure metric: NASA has ostensibly used the metric system since about 1990, the statement said, but English units are ...

4

There are a couple of popular methods. One is the Darian calendar, which has 24 months of 27-28 sols, with month names based on constellations. More of them are discussed in the Martian Timekeeping article. The "Official" means is the angle from Solar Angle 0 crossing, measured 0-360, which can tell the season and other items.

3

Big organisations have big cracks for things to fall down. NASA has the additional problems of: There not being much precedence for most of the things they do. They only getting one shot at it most of the time. In such case the big ticket items, are typically well taken care of. If it's clear what the question is and there is the potential for get it wrong ...

3

Units are always a challenge, and when you think you've got it right it's also important to check them with dimensional analysis. Sometimes people calculate orbits in dimensionless units, so for example with $\mu=1$ and $a=1$ the period is just $2 \pi$. If you have two massive bodies then $\mu_1 + \mu_2 = 1$. But when we're doing thins with real world ...

3

According to Wikipedia foot-pound and foot-pound-force are synonymous: The foot pound-force (symbol: ft⋅lbf or ft⋅lb) is a unit of work or energy in the Engineering and Gravitational Systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of ...

1

Everything I've seen from Mercury to Apollo has been in imperial units but that doesn't mean they used metric and converted it all over before handing it over. There is a pretty good article here that talks about the Apollo guidance computer. The computer was programed to use SI units, which is basically metric with a new name, but everything entered into it ...

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