Spacecraft Launch Systems

Saturn V launch

Saturn V compared to N1

A launch system is a system that allows a spacecraft to reach orbit above the surface of the Earth or a celestial body such as the Moon, Mars, an asteroid (such as Ceres). It includes the launch vehicle or vehicles, the launch pad, and other infrastructure. For the US Apollo program to the Moon the launch system included a Saturn V rocket and launch pad 39 at Kennedy Space Center. For the USSR Zond program to the Moon the launch system included a Proton UR-500 rocket from the Baikonur Cosmodrome. For the USSR N1/L3 program to the Moon the launch system would have included an N1 rocket from the Baikonur Cosmodrome.

All of these launch systems used liquid propellants, but they didn't use the same propellants. The Saturn V first stage was fuelled by RP-1 (a mixture) and liquid oxygen or LOX (O2). The second and third stages were fuelled by liquid hydrogen (H2) and liquid oxygen or LOX (O2). The Proton is fuelled by very toxic unsymmetrical dimethyl hydrazine or UDMH (H2NN(CH3)2) and dinitrogen tetroxide (N2O4) which ignite on contact. The N1 was to be fuelled by RP-1 and liquid oxygen or LOX.

In addition to Apollo, Zond, and N1/L3 programs, other launch systems have successfully launched autonomous spacecraft that safely landed on the Moon or went into orbit around the Moon. These include the Atlas Centaur, Molniya-M, Delta II 792X, Atlas V, Long March, SLS, and others.

These launch systems also used liquid propellants. They mostly use the same combinations of propellants as the Saturn, Proton, and N1, although some used Aerozine (A-50) rather than unsymmetrical dimethyl hydrazine (UDMH). However, in addition to liquid propellants, some of these launch systems used solid propellant rockets. These solid propellant rockets quite often used powdered aluminium as a fuel, but might use magnesium or zinc. Additionally they will have an elastomer binder such as hydroxyl-terminated polybutadiene (HTPB) or polybutadiene acrylic acid acrylonitrile prepolymer (PBAN) both of which additionally act as lower energy fuels. For an oxidizer they most often use ammonium perchlorate (AP), thus being refered to as ammonium perchlorate composite propellants (APCP). Solid propellant rockets generate lower specific impulse (Isp) than liquid propellant rockets. While liquid hydrogen and LOX might have an Isp of 450, and RP-1 and LOX might have an Isp of 350, a solid propellant rocket might have an Isp of 250.

Launch systems used for Lunar missions
Launch Vehicle	mission type	country of development	payload to LEO (kg)	payload to GTO (kg)
Ariane 5G	Lunar orbit	Europe	18,000 LEO	6,950 GTO
Athena II	Lunar orbit	USA	1,800 LEO	593
Atlas SLV-3 Agena-D	Lunar orbit	USA		700
Atlas SLV-3C Centaur-D	Lunar landing	USA		2,222
Atlas V 401	Lunar orbit	USA	9,050 LEO	4,950 GTO
Delta II 792X	Lunar orbit	USA		1,819 GTO
H-IIA	Lunar orbit	Japan		4,100 to 6,000
Chang Zheng 3 aka Long March 3A	Lunar orbit	China	6,000 LEO	2,600 GTO
Chang Zheng 3B aka Long March 3B	Lunar landing	China	11,200 LEO	5,100 GTO
Long March 5	Lunar landing	China		14,000 GTO
Minotaur V	Lunar orbit	USA		532
Molniya-M	Lunar landing	USSR, Russia	2,400 LEO	1,600
Mu-3S-II	Lunar orbit	Japan	770 LEO	520
UR-500K aka Proton-K/D	Lunar landing	USSR, Russia	19,760 LEO	4,930 GTO
PSLV-XL	Lunar orbit	India	3,800 LEO	1,425
Saturn V	Lunar landing	USA	140,000 LEO	48,600 to TLI
Titan II(23)G	Lunar orbit	USA	3,600 LEO	> 3,000 ?
SLS	Lunar orbit	USA

In addition to the rocket propellants, a launch vehicle has chemical rocket engines that burns the propelants creating a lot of pressure in the rocket engine combustion chamger. This pressurized gas is guided by the rocket engine nozzle into a high-speed exhaust stream which causes the rocket acceleration. While a liquid propellant rocket engine may use pumps to feed the propellants into the combustion chamber, solid propellant rocket engine combustion chambers are formed out of the solid propellant itself.

Probably the smallest rocket used for a Lunar mission was the Mu-3S-II which was used to send the Japanese Hiten spacecraft to the Moon... although there were issues with getting all the way to the Moon. The Mu-3S-II was a four stage all-solid rocket engine launch vehicle. It had a diameter of 1.41 m and a height of 27.80 m. It's gross mass was 61,700 kg. Two other launch vehicles used for Lunar missions similar in size to the Mu-3S-II were the Athena-2 used for the Lunar Prospector spacecraft and the Minotaur V used for the LADEE spacecraft. The Minotaur V launch vehicle was derived from retired Peacekeeper ICBMs. Both of these launch vehicles had a larger diameter and were more massive than the Mu-3S-II. There are teams, some listed below, competing to put tiny satellites into orbit. However, they are not trying to get to the Moon, just to orbit, and they are working in teams and launching from safe locations.

Rockets use various methods to compensate for air turbulance and adjust their direction of flight. This might include fins on the outside of the rocket, vanes in the engine exhaust stream, or gimballed engines which can change the direction of the nozzle. To control these mechanisms the rocket might have an electronic guidance system. The Saturn V had a section called the Saturn V Instrument Unit. This unit included the ST-124-M3 inertial platform, and the launch vehicle digital computer (LVDC). Note that the LVDC is not the same as the Apollo Guidance Computer (AGC) which was used both in the Apollo Command Module and in the Apollo Lunar Module.

The Delta II booster is controlled by the second-stage avionics system which provides guidance, flight control, and vehicle sequencing functions during the booster and second-stage phases of flight.

Working Example

For students who want to experiment with a working example, you probably shouldn't be experimenting with LOX and certainly not with UDMH nor dinitrogen tetroxide, so if you want to experiment with rockets, what should you do? As mentioned above, in addition to liquid propellants, rockets can use solid propellants. The Space Shuttle used two solid propellant boosters, and the Titan IIIE Centaur, Delta II 7925, and Atlas V 541 also used solid propellant rockets along with their liquid propellant rockets. The Scout launch system was the first orbital launch vehicle to be entirely composed of solid propellant rockets. More recent launch vehicles that use mostly or all solid propellant rockets to launch spacecraft into orbit around the Moon include the Athena II, Minotaur V, and Mu-3S-II. The Minotaur V is a 5 stage launch vehicle composed entirely of solid propellant rockets, and it's first launch was used to put the Lunar Atmosphere and Dust Environment Explorer (LADEE) into lunar orbit.

The job of a launch system is to accelerate a spacecraft horizontally to orbital velocity. However, before doing this, the spacecraft must be raised to an altitude high enough that it won't experience significant atmospheric drag or run into mountain tops on planets without an atmosphere.

Many lower power solid propellant rocket engines are available commercially. These won't get you to orbital velocity nor will the get you above Earth's atmosphere, but they can be educational. These can be fuelled with black-powder or with ammonium perchlorate composite propellants similar to what was used in the solid propellant rockets of the Space Shuttle. Some sources of solid propellant model rockets include:

Before launching your rocket, you should have an estimate of how high your rocket will go. The altitude a rocket will go depends on its velocity, the velocity depends on its acceleration, and the acceleration depends on the rocket thrust and mass. The drag of the rocket through the atmosphere also affects its altitude. Determining the altitude a rocket will go is a little hard because the mass of the rocket changes as the rocket fuel is consumed. To estimate the altitude and velocity your rocket will fly, download the Android RocketCalc app to your Android smartphone.

Run RocketCalc and select the Options (or Parameters) menu item. Enter into RocketCalc the characteristics of your rocket and rocket engine and select OK. RocketCalc will then display the likely flight profile of your rocket. You can tap on the RocketCalc flight profile screen to find the altitude and velocity at any particular time during the rockets flight.

Finally, if you are interested in launching a CubeSat into orbit rather than just experimenting with your own rocket, the following is a list of launch service providers that will launch CubeSats:

While a CubeSat launch will get you to orbit , it will be a low Earth orbit (LEO). If you want to get to the Moon, you would need a propulsion system on your CubeSat, such as a rocket , in order to raise it's orbit. However, things that may explode like a liquid propellant or solid propellant rocket may make the launch provider nervous, and some don't accept CubeSats that have them. Alternate propulsion systems like cold gas, resistojets, electrospray, vacuum arc thrusters, and ion thrusters have flown on CubeSats. Also, solar sails have been proposed to be flown on CubeSats. However, all of these typically have less instantaneous thrust than typical rockets.