Why did the Space Shuttle have an indicator to alert the crew to the arming of the range safety destruct system? Quoting from here:

The first message, called arm, allows the onboard logic to enable a destruct and illuminates a light on the flight deck display and control panel at the commander and pilot station. The second message transmitted is the fire command.

This seems, er, rather grim. Why is this light there?

Edit: Perhaps it is used for testing purposes - can anyone provide a reference for whether this indicator was used by the crew or ground personnel during pre-flight checkout? Second idea is that it was to alert the crew to accidental arming, however since the command decoders appear to have used some type of encryption this seems unlikely to have occurred accidentally by remote. If the range saftey system had become armed by an internal vehicle fault, is there anything the crew could have done about it?

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    $\begingroup$ Seems unlikely that it would be used for testing purposes - and I would agree that if I were an astronaut I would certainly prefer not to know it's coming. $\endgroup$ – Undo Nov 2 '13 at 22:23
  • $\begingroup$ Could "armed" simply mean "ready to receive and act on any destruct order"? Like switching off the safety on a firearm? $\endgroup$ – DJohnM Nov 3 '13 at 3:10
  • $\begingroup$ @User58220 Yes, presumably that is exactly what the indicator means. Is arming the destruct sequence a standard part of the launch sequence, or would it be armed only immediately prior to the destruct command being issued? My guess would be the latter, but I'm not sure. $\endgroup$ – Bitrex Nov 3 '13 at 4:34

I think I may have found a possible answer. The control panel for Columbia had the indicator:

Columbia panel

The control layout for Discovery (and presumably the other orbiters as well) was somewhat different, and does not have the indicator:

enter image description here

Given that Columbia was originally fitted with ejection seats, in that context the indicator seems to make more sense.

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    $\begingroup$ What you are point out is not a Columbia-Discovery difference, you are looking at the difference between the original instrument panel and the MEDS instrument panel, which was introduced in the early 2000s. All of the shuttles originally had the top panel. $\endgroup$ – Tristan Nov 8 '13 at 19:54
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    $\begingroup$ "The control layout for Discovery (and presumably the other orbiters as well) was somewhat different, and does not have the indicator" I don't think so. IIRC the indicator was moved in other place. In Space Shuttle Mission Simulator (it simulates modern cockpit of Space Shuttle) there is one its below commander's HUD near HUD data bus switch. $\endgroup$ – nonamedtechie Jan 25 '15 at 19:44
  • $\begingroup$ While it is true that the cockpit layout was redesigned, the indicator was not removed, just relocated. $\endgroup$ – Organic Marble Jul 17 '19 at 16:50

The Range Safety Armed light was a cue for the crew to eject during the Orbital Test Flight period of the Shuttle program. After the ejection seats were removed from Columbia, the light was still there.

See Space Shuttle Range Safety System in the Rogers Commission Report.

The location of the indicator changed after the Orbiter 'glass cockpit' upgrade, but it was in the vehicles until the end of the program.

enter image description here enter image description here

(Personal photo taken in Orbiter cockpit in May 2008, drawing from SCOM, see link below)

For the latter part of the program, the only Range Safety System left on the stack was in the Solid Rocket Boosters. So if Range Safety actions had to be taken in 2nd stage, the illumination of this light served as a backup or no-voice-comm cue to the crew to take the actions they had been briefed on.


During first-stage, trajectory deviations may lead to a violation of a destruct line by a shuttle that is still under control. It may be possible to return the vehicle toward its nominal trajectory or to safely execute an abort. Therefore, the Flight Director (FD) and Flight Dynamics Officer (FDO) are in voice communication with the Flight Control Officer (FCO) (formerly Range Safety Officer) during ascent. If the FCO detects a violation, the FDO and FD are immediately informed. The FD must determine whether the shuttle is controllable or uncontrollable, and inform the FCO. As long as the FD declares the shuttle controllable, the FCO takes no action to terminate the flight for trajectory deviations alone.

Range Safety Limit Avoidance

A deviation from nominal trajectory that is large enough to warrant FCO action must be corrected. First-stage options are:

• State vector update

• Select CSS (after 90 seconds MET)

• Engage BFS

In second stage, the options are:

• State vector update

• ATO selection

• Select CSS • TAL or RTLS selection

• Engage BFS

• SSME manual cutoff. For loss of comm, FCO will send the ARM command as a cue for manual MECO

Options are listed in order of priority. The priorities are established such that higher priority options preserve lower priority options and involve fewer new dangers to the crew and shuttle when possible.

Source: Shuttle Crew Operations Manual, page 6.2-5 (emphasis mine)


I can’t speak about the use of the arm indication early in the program but it was used for a time to indicate the crew should shut down the main engines in a comm out situation. It was utilized in this role per Shuttle Range Safety Mission Rules, until the Range Safety Flight Termination System (FTS) was removed. After that time and until the end of the Shuttle Program, an Arm Command was immediately followed by a Fire Command for that period of SRB flight and USAF Range Safety initiated main engine shutdown, if required, was initiated via verbal communication from the Flight Director. A JSC lead Flight Dynamics Officer and I (a USAF Range Safety Officer) were responsible for the Shuttle Range Safety Destruct Criteria from 1992 through 2008.

  • $\begingroup$ Should have stated the ET Range Safety System was removed $\endgroup$ – Michael Campbell Jan 27 '19 at 18:02
  • $\begingroup$ You can click edit and adjust your own post any time! That's much better than correcting yourself in comments. If you can add any links supporting your answer as well, that would be even better. Welcome to Space! $\endgroup$ – uhoh Jan 28 '19 at 1:29

The Range Safety System is armed as part of the launch countdown sequence. You can hear, "Range Safety System is armed," at about the 14-minute mark in this launch video for STS-83. (


According to Wikipedia (https://en.wikipedia.org/wiki/Range_safety), the solid rocket boosters and the external tank were armed with the capability of being blown up, but not the shuttle orbiter itself.

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    $\begingroup$ Doesn't answer the question "Why is there a caution light?" $\endgroup$ – Organic Marble Jul 17 '19 at 19:05

Here is a cockpit photo from Wikipedia. I added some labels to show what some of the switches and buttons doing.

I am showing the new location of RANGE ARM SAFE light.

enter image description here

And if I would be an astronaut I would like to know what is going to happen with me.

EDIT: http://history.nasa.gov/rogersrep/v1ch9.htm This explains a lot.

First of all SRB may hang out on aft attachment points when you try to jettison them while they still provide thrust... But when SRBs are burned out you can do a fast separation and quickly separate the ET from shuttle.

Looks like that this not confirms that shuttle itself has a charges. On this picture you can see only SRB and ET linear charges. Note that IIRC charges on ET was later removed.

Since the current range safety system does not allow for selective destruction of components, the Commission believes that NASA and the Air Force should critically re-examine whether the destruct package on the External Tank might be removed.

Looks like i was wrong and there is no selective destruct. Now after ET charges was removed probably only SRB have charges as they are most dangerous because of uncontrollable flight when detached from rest of package.

And OFC there is no need for charges inside shuttle itself as its the safest part of whole package. It's rather predictable, the thrust of SSME can be terminated by command, it had not so much dangerous fuel.

The ET itself is quite dangerous, its flight is predictable but when it hit ground there will be huge explosion. IMO the decision to remove charges from ET was not so good. Implementing selective destruct would be much better IMO.

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    $\begingroup$ You can always edit your other answer. $\endgroup$ – HDE 226868 Jan 25 '15 at 21:02
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    $\begingroup$ Tinypic hosted image has no information on the authorship / source. The light identified as Range Safe Arm (with a "you have really bad day" comment) is in real life designated "CDR2" and it has a toggle switch next to it with a label "HUD DATA BUS". That doesn't seem to me like anything that you're describing. See e.g. in this 360 panorama view. $\endgroup$ – TildalWave Jan 25 '15 at 21:22
  • $\begingroup$ CDR2 is a label to switch, not to light. Lights in Space Shuttle has no labels. Look at your panorama, look at light and you will see the RANGE SAFE ARM written on the light, its bearly visible but it is! $\endgroup$ – nonamedtechie Jan 25 '15 at 21:26
  • $\begingroup$ Oh sorry. Its not label to switch, its label for display. CDR2 means second commander's display :-) And take zoom at this light in this panorama, you will see RANGE SAFE ARM, its really there but its bearly visible. $\endgroup$ – nonamedtechie Jan 25 '15 at 21:31
  • $\begingroup$ You're right, I missed that. Still, can we please focus on answering the question in your now two answers? Note that there's both edit and delete links displayed under them. Please select one to keep and answer the question. Contradicting yourself in new edits isn't really helpful, it just wastes everybody's time reading it. Thanks! $\endgroup$ – TildalWave Jan 25 '15 at 21:34

It would be armed prior to destruction, not as part of launch sequence but only in emergency. Don't forget that, in theory, it's possible to bail out before the RSO (Range Safety Officer) initiates self-destruct.

So if the crew see this light, they can always try to bail out. And astronauts should be always informed about everything, just like airplane pilots and soldiers on battlefield.

  • $\begingroup$ Wouldn't the crew be aware of the reason for the system to be armed even without the light? If you're hurtling towards a populated area (unlikely), you'll realize it without the system. You'll either have time to bail out or you're in trouble. $\endgroup$ – HDE 226868 Jan 4 '15 at 18:25
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    $\begingroup$ AFAIK there is no provision for the crew to "bail out" on ascent. The Inflight Crew Escape System was only designed for unpowered, gliding flight: spaceflight.nasa.gov/shuttle/reference/shutref/escape/… $\endgroup$ – Bitrex Jan 4 '15 at 20:32
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    $\begingroup$ @HDE226868 If things have gone badly enough wrong that you're heading for a city you very well might not have enough information to know where you're going. At that point you almost certainly know there's no hope, though--a shuttle crash is much worse than an airplane crash. It's runway or die. $\endgroup$ – Loren Pechtel Jan 7 '15 at 2:33
  • $\begingroup$ I don't know why you think that soldiers on a battlefield are informed about everything. I trust that my commander has more information, but the common soldier knows pretty much nothing other than "other good guys somewhere in that direction, civilians in that direction, bad guys suspected in all directions". $\endgroup$ – dotancohen Jun 8 '15 at 12:07
  • $\begingroup$ The crew couldn't bail out on ascent after STS-4. $\endgroup$ – Organic Marble Jul 17 '19 at 19:06

Don't forget that you can always shut down engine to terminate thrust (its possible from ground and there are also button in cockpit, those buttons are on center panel between commander's and pilot's seats).

SRB can be jettissoned, normally its automatic but you can also do it manually in emergency (using ground command and there is switch + button on center panel between seats).

ET (External Tank) can also be jettissoned manually (switch + button on center console between seats, i am not sure about ground command).

So its very easy to terminate thrust and turn this "rocket" into glider then blow SRB away from Space Shuttle itself.

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    $\begingroup$ nonamedtechie welcome to Space Exploration! I'd like to ask of you to read our About and specifically How to Answer, because while your contribution is interesting, it also seems more of a comment than an answer to the question asked at the top of the page. Note that we're a Q&A and not a discussion forum, and this is how we organize things around here. A question, followed by as complete and standalone answers as possible, preferably providing references for claims made. Please edit to address also main points of the question and include links / quotes, if you can provide some. Thanks! $\endgroup$ – TildalWave Jan 25 '15 at 20:24
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    $\begingroup$ Agreed, I don't quite see the link to the range safety system (which could presumably destroy the entire Shuttle stack). $\endgroup$ – Hobbes Jan 25 '15 at 20:26
  • $\begingroup$ Doesn't answer the question "Why is there a caution light? $\endgroup$ – Organic Marble Jul 17 '19 at 19:06

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