Building reusable rockets

**Reusable rockets** are rockets that can be recovered , refurbished and reused after landing. Usually, they are recovered using engines or parachutes. Because of the impracticality of refueling rockets in SFS outside of a zero-G environment, combined with few to no possibilities of refurbishing a rocket, a reusable rocket in SFS is usually defined a rocket that can safely land on the Earth after it has fulfilled its purpose and be recovered.

**Note:** Most "reusable" rockets in SFS are never brought back to the Space Center for refueling and restaging due to the difficulty required to do so. This is why most "reusable" rockets are actually only **recoverable**.

## How to build?

To build this type of rocket, you need several parts:

1. Engines
2. Separators
3. Landing legs
4. Fins, preferably grid fins (for more aerodynamics; can only be used in landing; neither available in-game)
5. Fuel
6. Fairing
7. Rcs Thrusters

### Engines

Start with the engines. You can use Hawk, Frontier, Valiant, or Titan. Hawk/Titan engines can be for a normal one and Frontier/Valiant is used for efficiency, but the low thrust of a Valiant limits its applications in boosters.

### Fuel

Now we need fuel in our rocket. You need to use some medium-sized fuel tanks (8-wide) for this. They can be clipped to engines like this:

Now you can skin them (assuming you have the skin expansion) to any colour like orange, black, grey, metal or stripes. You can also use a combination of these.

Engine bases may also be used in constructing the fuel tanks, but this is optional.

### Landing legs

Now for landing legs. They are used to cushion the impact from the surface and protect parts of the rocket such as the engine(s), as landing legs can withstand impact velocities of up to 12 m/s, the second highest of any object in game. They are stowed at launch and deployed when landing occurs. You can use any style of landing legs, however make sure that the landing legs provide enough stability for the rocket, as not all terrain is flat. SpaceX Falcon 9 style is recommended.

### Grid fins

Grid fins are used like heat shields in atmospheric entry and landing to be more aerodynamic. It can be also used for stabilizing the rocket in landing. They are extended when it is in the upper layers of the atmosphere.

There are no grid fins in the game yet so the best option is to use stowed landing legs and clip them on the side of the fuel tank.

### Separator and second stage

Now it needs to have a second stage for space activities. Put a separator on top of the first stage, and repeat the steps above, but this time use a vacuum engine (Frontier/Valiant engine) and a shorter fuel tank.

### Fairing

If it carries payloads to space, it needs a fairing. Attach it to the top of the second stage, and skin it.

### RCS thrusters

They can be represented as reaction wheels when landing a first stage.

### Payload adapter

You're almost complete! To hold the payload on top of the rocket, it needs some adapter. Place a separator/docking port and you're done!

### Other parts

It is advised to use a probe on the first stage so you can control it, as a uncontrollable stage usually cannot be safely landed. Parachutes can be used on the first stage instead of grid fins, if you are not good at suicide burns.

Docking ports can be used instead of separators for payload adapters. The same is applied for interstages between the first and second stages, with a fairing to be used to cover the engines on the second stage.

## How to use it?

1. Turn on the first stage engines and throttle up to 100%.
	1. If the TWR of the rocket is high, the throttle must be below 100% to reduce aerodynamic resistance during max q.
2. After 500 meters, turn slowly to one side.
3. When the first stage's fuel drops to 30% or lower, separate it. If it uses parachutes then separate it when it runs out of fuel.
4. Continue going on. Turn on the second stage engine and get to orbit.
5. After the second stage has gone to orbit, switch to the first stage.
6. Deploy the grid fins and burn the engine until the velocity drops to around 200 m/s (at 250 m/s, heating begins).
7. If your rocket speeds up to 350 m/s before reaching the lower atmosphere, burn back to 200 m/s.
8. Repeat until at lower atmosphere, at which point you must decelerate to less than 250 m/s and coast (you may also use a heat shield, but this is not reliable, as it can cause dangerously high speeds because of a high sectional density, that is hard to survive even with parachutes as your velocity will be too high to deploy them before you crash, unless you have a suitable (shallow/long) re entry profile and stabilizing heat shields).
9. If it uses parachutes, deploy them as soon as possible (2500m).
10. Deploy the landing legs at a altitude of around 1000m.
11. If it is a VTVL, do either a suicide burn, or decelerate progressively.

## Examples

* Falcon 9
* Falcon Heavy
* Super Heavy Booster and Starship

## Gallery

A reusable rocket during launch.A first stage of a reusable rocket during atmospheric entry. It uses grid fins to stabilize the descent.A reusable rocket's first stage landed on a side of a depression.The second stage of a reusable rocket releases its payload.A Falcon 9 launch.A Falcon Heavy launch.A Falcon 9 first stage landed on a drone ship in the middle of the Atlantic ocean.

### List of your reusable rockets

#### Mermaid 4.5

Mermaid 4.5 is a rocket part of the Mermaid 4 series, it doesn't need to use grid fins as it's navigation system for landing. It can land on the Distanian Landing Pad, Distanian Sea Landers (*Mermaid on Rock, Lovely Ending, Seashell*)

#### Mermaid 5.0

The Mermaid 5.0 is a reusable rocket part of the Mermaid 5 series. Instead of landing legs it uses some sort of "fins" to land.

#### Example

Used in the top of this page, this rocket can carry up to around 50 tons of weight to space. It has 2 stages. The first stage can carry the rocket to a suborbital trajectory with its apogee reaching 33 kilometers or less. It has 3 engines. Two of the engines can be turned off during landing. There are landing legs that can cushion the landing. There are 4 grid fins that can be used during landing. The second stage will carry it to space. The payload will be then release after a couple of burns to get to the destination. The fairing sits on top of the second stage and is detached after the second stage fires its engines for a couple of seconds, usually when it's out of the atmosphere.

#### Ultraheavy Launch Vehicle or "Superstarship"

An 8500 ton behemoth that can be recovered and reused. The rocket consists of two stages: the Booster and the Orbiter. First the Booster boosts the Orbiter until the Booster's fuel percent reaches 15%, then the Booster separates from the Orbiter which fires up its 67 vacuum engines and continues to orbit. The Booster then slows itself down and deploys its parachutes and landing legs, were it lands about 2 kilometers away. The orbiter then reaches the desired orbit, opens its cargo bay, and deploys the payload. The Orbiter then deorbits, reenters horizontally, the flips to engine side down, and propulsively lands.

Vehicle Stats
 Expended

#### **RB-2**

The RB-2 is a rocket part of the RB-X series [ rockets of bulgaria ]. It consist of two liquid rocket booster [ LRB ] and one custom-made second stage that size depend on cargo size thus making each launch different. The boosters togheter weight 450 tons and payload mass into orbit can be up to 100 tons but can go over it [ if used another stage ]. The booster and stages are reusable and expandable but atleast 10% are required the booster fuel to be left so that it can slow down and survive re-entry. The second stage depends how it will land but the booster have landing gears on the side and lands horizontally which increase drag slowing down the rocket unlike vertical landing.