Since solid-fuel rockets can remain in storage for a long time without much propellant degradation, and the fact that they almost always launch reliably, they have been frequently used in military applications such as missiles. The lower performance of solid propellants (as compared to liquids) does not favor their use as primary propulsion in modern medium-to-large launch vehicles customarily used to orbit commercial satellites and launch major space probes. Solids are, however, frequently used as strap-on boosters to increase payload capacity or as spin-stabilized add-on upper stages when higher-than-normal velocities are required. Solid rockets are used as light launch vehicles for low Earth orbit (LEO) payloads under 2 tons or escape payloads up to 500 kilograms (1,100 lb).
After separating from the command module in lunar orbit, the LM Antares had two serious problems. First, the LM computer began getting an ABORT signal from a faulty switch. NASA believed the computer might be getting erroneous readings like this if a tiny ball of solder had shaken loose and was floating between the switch and the contact, closing the circuit. The immediate solution – tapping on the panel next to the switch – did work briefly, but the circuit soon closed again. If the problem recurred after the descent engine fired, the computer would think the signal was real and would initiate an auto-abort, causing the ascent stage to separate from the descent stage and climb back into orbit. NASA and the software teams at the Massachusetts Institute of Technology scrambled to find a solution. The software was hard-wired, preventing it from being updated directly. The fix involved indicating that abort mode was already active, so that if the signal were to arise again, it would be ignored rather than initiating what would have appeared to the software to be a second abort. The software modifications were transmitted to the crew via voice communication, and Mitchell manually entered the changes (amounting to over 80 keystrokes on the LM computer pad) just in time.
The Solar System formed 4. 6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.