I apologize for the completely opinion piece but I am horrified at what I see as a complete lack of understanding regarding the launch scenario. Apparently because SpaceX (and am not singling them out but they are the most recent example) had a launch result in an explosion people are misunderstanding where the blame lies. First of all I would without a doubt fly into space tomorrow – particularly if SpaceX were the carrier as I have more trust in SpaceX than any of the others.
Let’s look at the simplest problems that aren’t really problems encountered almost every time there is a launch! A common cause of delays – with anybody and everybody is weather. AND I am not even talking Space Weather (Solar Storms etc.) I don’t know if NASA still does this but know that only a few years ago they did – send up weather balloons just prior to a launch as well as utilize Doppler radars, weather radars, probably the GPM satellite, but NASA does everything it can to know every little detail to prevent unknowns. (Remember Algebra & Geometry in school? No one likes unknowns!)
Conditions for a launch need to be ideal as the launch is already so dangerous that whatever problems can be eliminated – need to be!
The following criteria are necessary to commit to a launch:
1) The temperature for the past 24 hours must be 41 degrees or greater. It CANNOT fall below 33 degrees for any period of time during that 24 hours.
2) Much as it cannot be cold, it also must not exceed 99 degrees for more than 30 minutes during that 24 hour period.
3) Additionally there can be no lightening nearby for at least 30 minutes.
4) The wind must stay below 19 to 24 knots. Stay below a range? Yes – it depends on the direction. ALSO- the wind is not sampled at ground level; it is measured 60 feet above the ground - at the launch pad.
Those are the simple constraints or criteria for a launch. Another cause of delays when the sensors alert the ground crew to an anomaly; Consider that there are many different spacecraft – Landers, shuttles, flyby spacecraft (manned & unmanned), orbiter spacecraft (also manned & unmanned), and on and on, so I’m just going to mention some of the systems since they will vary with each spacecraft.
First there is a structural subsystem. The spacecraft bus is a major part of the structural subsystem of a spacecraft and provides a place to attach components internally or externally, and to house delicate modules requiring a measure of thermal and mechanical stability. It is an integral card chassis for supporting the circuit boards of radio equipment, data recorders, computers, gyroscopes etc. The bus also establishes the basic geometry of the spacecraft, providing the attachment points for external items such as booms, antennas and scan platforms.
Then there are the Power supply systems. First this will depend on the type or types of power utilized, duration of the mission comes into play, and the where of it al matters greatly. Keep in mind that some systems are not powered on until different points in the launch and so any problems from faulty connections to switches to any other little thing which could then lead to a big thing!
Some of the various systems under this heading are;
Batteries-Devices with two or more connected cells that produce a direct current by converting chemical energy into electrical energy. Due to their short lifetime, batteries are only used when a very short operating life is required.
Photovoltaic cells: Crystalline wafers, called solar cells, which convert sunlight directly into electricity without moving parts. These cells are grouped into an array and cemented onto a substrate. The resulting assemblies are called solar panels or solar arrays. Solar power is practical for spacecraft operating no farther from the sun than about the orbit of Mars.
Radioisotope thermoelectric generator: A device that converts the heat produced by the radioactive decay of plutonium-238 into electricity by an array of thermocouples made of silicon-germanium junctions. They are used when a spacecraft must operate at significant distances from to sun (usually beyond the orbit of Mars). The Pu-238 is contained within a crash resistant housing.
Fuel cells: Cells in which chemical reaction is used directly to produce electricity. The reactants are typically hydrogen and oxygen which results in water as a by-product. The water can then be used for cooling and human consumption. Fuel cells are generally used on manned spacecraft.
Obviously communications are necessary if it is manned but they are also required in unmanned or autonomous spacecraft to send data. There often are; a high gain antenna, low-gain antenna, medium-gain antenna, a transmitter, and a receiver. (Frequently, transmitters and receivers are combined into one electronic device which is called a transponder.) Keep in mind that each of these has all sorts of connections and other things where each individual one could have a problem.
When it comes to interpreting commands from Earth or collecting and processing the telemetry data before passing it back to Earth as well as managing other subsystems and communicating their status’ the onboard computer is responsible for a lot.Systems maintained by this ob-board computer are:
The Spacecraft clock: A counter maintained by the command and data subsystem(On-Board Computer). It takes note of the passage of time – often cueing certain systems when to initiate, it also regulates nearly all activity within the spacecraft systems. Many types of commands uplinked to the spacecraft are set to begin execution at specific spacecraft clock counts.
Telemetry: The system for radioing information from a spacecraft to the ground. Telemetry is typically a mixture of science data from the experiments and spacecraft engineering or health data. Engineering or health data is composed of a wide range of measurements, from switch positions and subsystem states to voltages, temperatures and pressures. Telemetry may be transmitted in real time, or it may be written to a data storage device until transmission is feasible.
Tape recorder: It really is a digital recording device, that is a device on magnetic tape and for playing back the recorded material. The stored data can be played back for downlink when receiving station resources are available.
RAM: Random access memory, the solid-state equivalent of a tape recorder. Banks of RAM can store large quantities of digital information without any moving parts.
Fault protection: Algorithms, which normally reside in more than one of a spacecraft's subsystems, that insure the ability of the spacecraft to both prevent a mishap and to reestablish contact with Earth if a mishap occurs and contact is interrupted.
Now we get to Attitude and Articulation Control – two very distinct and important things. Besides being important to communications (so that its high-gain antenna may be accurately pointed to Earth) it important to heating and cooling/thermal control sub-systems, Spin Stabilization – using gyroscopic actions, three axis stabilization(Stabilization accomplished by nudging a spacecraft back and forth within a deadband of allowed attitude error, using small thrusters or reaction wheels), Reaction Wheels – you’ve heard of them as many space telescopes or cameras onboard various spacecraft have them: they are electrically-powered wheels mounted in three orthogonal axes. There is also the Attitude and articulation control subsystem which is an onboard computer that manages many of the tasks that rely on movable appendages such as solar panels, high gain antennas or optical platforms, but also star trackers, solar trackers, planetary limb trackers and many more.
I could continue but besides it being several more pages – note- I haven’t even gotten to the engine/propulsion system as of yet, you likely understand what I am getting at. While this is big picture stuff, and I haven’t even scratched the surface of mentioning all the components such as O-rings (memory alert), what I am saying is there are many things that make up a spacecraft. That alone would be a lot to worry about but now add in the many things that make up our atmosphere, the many different levels with different make-ups. Now throw in each individual thing that could make a difference, from a bird to a cloud…there are quite literallymillions of things that could go wrong, and yet spacecraft make it up a good percent of the time. Used to be, and not that long ago, that one out of three launches was pretty good, SpaceX completed 6 of 7 and the 7thlasted until it went supersonic, damn their good!
So let’s cheer for all the cool launches we see and be glad that recent accidents involved autonomous flights so no humans were harmed.
OH – AND WHILE I’M AT IT? I wouldn’t mind seeing the launches covered on regular TV. Carrying only the bad part of space is like covering only bus crashes and then telling your kid to go to school! Besides, they’re really cool! (KUDOS TO MSNBC for doing just that lately – covering launches! Way to go!!)