# Did some of the Shuttle fuel tanks actually orbit?

In Buzz Aldrin's book Encounter with Tiber, he mentions that some of the Space Shuttle's fuel tanks actually made it to orbit. Did this actually happen, and if so, for how long did they stay in orbit, and what altitude did they achieve?

• – called2voyage May 12 '14 at 19:10
• Technically, some of the tanks did make it to orbit - the OMS and RCS tanks built into the orbiters. – Sean Feb 24 '19 at 4:42

Based on this description of the Space Shuttle flight profile, no external tank would ever have completed so much as a single orbit. An external tank would achieve essentially the same orbital apogee as the orbiter itself, but that is all. The shuttle fired its OMS engines to achieve an actual orbit AFTER tank separation. This means that the tank remained on a trajectory which would intersect (re-enter) the atmosphere with no chance of ever completing an orbit.

The only way an external tank could remain in orbit would be if it was left attached until after the orbiter had completed its OMS burns to establish an orbital trajectory. To do so would increase the mass to which the OMS engines must apply the required delta-V... by more than the vehicle's payload capacity. This would require reducing, or more likely eliminating the internal payload. The upshot being that a shuttle flight in which a tank is inserted into orbit (if it were even possible) would be a mission to insert a tank into orbit and almost certainly accomplish nothing else. See this question for a more comprehensive analysis.

Aldrin has apparently exercised a bit of creative license; the title you mention is after all, a work of fiction.

• It would have been an interesting mission, regardless. You have to wonder how much the extra weight would have added to the total fuel needed. – user3323 May 10 '14 at 20:41
• @doz An empty external tank weighs about a quarter the loaded weight of the Shuttle, so to a first approximation, it'll increase the fuel requirement by 25% or so. – Mark May 11 '14 at 1:18
• @Mark which then in turn increases the mass by... which then increases the fuel... which then incr... – Magic Octopus Urn Aug 12 '18 at 21:24
• @MagicOctopusUrn, not really. Check the rocket equation: for a fixed change in velocity, a linear increase in payload mass requires a linear increase in fuel mass. Think of it this way: if a rocket with X fuel can throw payload Y into orbit, then two rockets each with X fuel can throw a total payload of 2Y into orbit. – Mark Oct 16 '18 at 22:36

There are generally speaking 2 conops to get into orbit with the Space Shuttle. The first one, and most commonly used, requires two thrusts post Main Engine CutOff (MECO) to achieve orbit. This one drops the ET in the Indian Ocean. The "Direct Insert" requires only one OMS maneuver, and the tank landed in the Pacific Ocean. So the External tank might technically have been in orbit briefly, but in a reentry orbit.

• Mneh. If PeA is negative, this isn't like being in orbit. – Deer Hunter May 11 '14 at 17:39
• It is like ballistic orbit, according to abyss.uoregon.edu/~js/space/lectures/lec05.html or ballistic trajectory astronomycast.com/2012/11/ep-277-orbit – osgx May 12 '14 at 12:10
• Eh, it's an orbit, just one that happens to intersect the Earth's surface :-) – Tristan May 12 '14 at 15:16
• I was more thinking upper atmosphere, which would drag it down enough to hit the Earth pretty quickly. – PearsonArtPhoto May 12 '14 at 15:17
• Direct insertion was the most commonly used method of space shuttle orbital insertion. – Sean Feb 1 '20 at 0:40