“Reusing the space launch vehicles, a leap in space exploration”

drishti-magazine

When Elon Musk’s SpaceX – short for

Space Exploration Technologies – got into the

rocket game, it promised reusability, lower

launch costs, and easier access to space. Over

the last few years the company has taken

steady steps to making good on that promise,

thanks in large part to the success of its Falcon

9 rocket.

The Falcon 9 is a two-stage rocket that’s

designed to launch satellites, and eventually

crewed spacecraft, into orbit. It stands 69.9m

tall, weighs 549,054kg, and generates 7,607

kilonewtons of thrust at take-off, which can send

22,800kg into orbit around the Earth.

Alternatively, it could send 8,300kg to Mars,

although it hasn’t launched anything to the Red

Planet just yet. Nonetheless, Mars is SpaceX’s

ultimate goal – Elon Musk has made no secret

of the fact that he wants to be the one to land

humans on our planetary neighbour.

In the meantime, SpaceX has more than 40

Falcon 9 missions into Earth orbit. The rocket

made history in 2012 when it became the first

privately launched vehicle to successfully send

a resupply mission to the International Space

Station, and has since added reusability to its

roster. This marks another step towards

SpaceX’s goal of sending humans into orbit from

American soil, something the world hasn’t seen

since the Space Shuttle’s final flight in 2011. But

it’s not just about NASA missions for the

moment. SpaceX’s launch manifest shows a

diverse roster of clients including the US Air

Force, national security missions, and

commercial satellite launches. All in all, SpaceX

is positioning itself to be a leading force as we

enter the new era of commercial spaceflight.

Falcon 9 relaunch

In April 2014, SpaceX signed a 20-year lease

to use NASA’s launchpad 39A, the very same

launchpad from which every Apollo mission

(other than Apollo 10) and a host of Space

Shuttle missions launched. To support the

Falcon 9 launch, SpaceX had to customise the

pad. It refurbished the sound-suppressing

deluge system, which uses water to protect the

rocket from its own acoustic energy at the

moment of launch. It also replaced electronic

components, power and plumbing lines, and

upgraded the liquid oxygen storage system that

is used to fill the rocket’s tanks before launch.

Octaweb mating

The metal Octaweb structure that houses

the Merlin engines is vital to the Falcon 9’s first

stage. Earlier versions of the rocket had nine

engines arranged in three rows of three. With

the Octaweb, eight engines are clustered in a

circle around a central one. The different engine

arrangement is more than just aesthetic. The

Octaweb reduces the length and weight of the

Falcon 9 thrust structure, simplifying the rocket’sdesign and assembly. Streamlining the

manufacturing process ultimately keeps launch

costs down.

Interstage

An interstage is vital to any multi-stage

rocket. This section connects the first and

second stages and also houses the engine of

the second stage, protecting it during the first

phases of flight. At the right moment, the

interstage separates the two stages, allowing

the second stage to fire safely. This is called

the ‘moment of staging’.

Separating rocket stages can be a tricky

business, but the Falcon 9 makes it simpler.

While the majority of rockets use a complicated

pyrotechnic system of explosive bolts to

separate stages, SpaceX uses an all-pneumatic

stage separation system. This system can be

tested on the ground, and also means staging

is less jarring to the rocket.

Merlin engine

The power behind the Falcon 9 is the Merlin

engine, which is built in-house by SpaceX. The

rocket boasts nine of these engines clustered

together in the first stage, while the second stage

contains a single Merlin that’s modified to fire in

the vacuum of space. These engines burn a

combination of rocket-grade kerosene called

Rocket Propellant 1 and liquid oxygen. On a

typical Falcon 9 launch, the first stage engines

burn for 162 seconds, and the second stage

engine burns for 397 seconds.

The Merlin engine is incredibly powerful and

one of the most efficient engines ever built.

Having nine of them in the first stage also offers

some built-in safety. On other rockets, if an

engine fails during launch, the lost thrust can

destroy the payload’s chance of successfully

reaching orbit. But the Falcon 9 is designed so

that two of the nine Merlin engines in the first

stage can fail and the launch won’t be affected.

The healthy engines can burn longer, pickingup the slack to save the mission.

Horizontal Integration Facility

SpaceX doesn’t build the Falcon 9 in Florida,

it’s just assembled there. Most of the rocket’s

parts are built elsewhere, notably on the other

side of the US in the company’s factory in

Hawthorne, California. This means the

components, including fuselages and engines,

need to travel around the US by truck to various

test stands before eventually ending up at

NASA’s Kennedy Space Centre in Florida.

Once in Florida, the pieces are mated in

SpaceX’s custom-build Horizontal Integration

Facility, a large hangar within sight of launchpad

39A.

First stage landing

The most exciting part of any Falcon 9 launch

might be the landing, specifically that of the first

stage onto a floating barge. The Falcon 9’s first

stage includes four small carbon-fibre landing

legs stowed flat against its fuselage. After the

rocket goes through staging, the first stage

begins its fall through the atmosphere. Cold gas

thrusters near the top flip the rocket around so

it’s upright. Then the stage engine fires briefly,

just enough to slow its fall. As the stage

approached its target, the legs deploy. In the

very final phases of its descent, three of the

nine Merlin engines fire one last time for what

A Falcon 9 rocket touches down

on one of the two offshore landing platforms

SpaceX calls the ‘boostback burn’. The stage

slows even further, almost hovering as it makes

a soft touchdown. This landing sequence

entirely automated, with the rocket stage

responding to real-time data.

Raptor Engine

The Raptor engine during testing

So far, the Raptor has not flown, and has

only been successfully test-fired on the ground.

Nonetheless, SpaceX has big plans for it. This

is the engine that will power eventual missions

to other planets, starting with Mars. The

company recently unveiled its design for a

planned interplanetary spacecraft, and in its

current incarnation uses a whopping 42 Raptor

engines in the launch vehicle’s first stage to getthis heavy spacecraft off the ground. But before

it launches to Mars, Raptor will make its debut

on an upgraded version of the Falcon 9.

Falcon 9 post-flight

After its successful landing, the Falcon 9’s

first stage is returned to the Horizontal

Integration Facility where it can be checked out,

refurbished, and readied for another launch.

Reusing the stage is much cheaper than

building a new one for every launch. The SES-

10 mission in March 2017 was the first time a

core stage of an orbit-capable rocket has been

reused, and the cost was “substantially less

than half” of what it would have cost to build a

brand new stage.

Elon Musk has likened single-use rockets to

single-use aeroplanes. If an airline had to scrap

a Boeing 747 after every flight, then the cost of

flying would be prohibitively expensive for the

average traveller. But aeroplanes aren’t singleuse,

they’re refuelled for another flight. If a

rocket can be refuelled like an aeroplane, then

the enormous cost of a spaceflight could drop

to a fraction of what it is now. And imagine the

implications of that!