http://www.humansinspace.org/wp/wp-content/uploads/2015/05/SpaceX-Cover-Page.jpg

2

SpaceX and the Quest for Rapid Rocket Reusability

We live in extraordinary times! We go out of our houses and

we in automobiles to reach distant destinations and we

catch airplanes to reach the other side of our beautiful

planet Earth

Image 1: McLaren supercar with an airplane’s jet engines in background

Imagine how people lived before we invented the

automobile and airplane. Imagine how people looked at the

first affordable car – Model T that Henry Ford built in 1908

and the first airplane that the Wright brothers invented in

1903.

Image 2: Henry Ford with the Model T – the first affordable car - 1908

Image 3: The Wright brothers with the first airplane - 1903

... And nowadays everybody has a car and everyone can

catch a plane for a rather reasonable amount of money. We

are literally like Greek gods …

Image 4: We live like Greek God from mythology

… We fly resting effortlessly in our comfortable (not on every

airline) seat.

Image 5: Some airplane seats are pretty comfortable

But it is in our human nature to explore new horizons and to

invent our future …

Image 6: Humans are always looking for a new frontier

What about reaching out even further and going one step

beyond. What about space?!

3 Of course, people have already gone to space! We have a

Space Station orbiting the Earth every hour and a half.

Image 7: The International Space Station 420 km above Earth

We have gone from the invention of the first airplane to

going to space and looking at our beautiful planet from the

Space Station in a matter of only 100 years! But how many

people have gone to space in total? – Only a little more than

530 so far! And how many thousands of us do fly on an

airplane each day? What is the cause of this difference? It

comes from the fact that going to space is expensive! Not

only expensive, it’s extremely expensive – to launch even

1kg to space costs tens of thousands of dollars!

Why? Because it

happens so that the

rockets that we build

and the fuel they

consume are

expensive! Why?

Because how many

times do you see any

particular rocket? Only

once! – At its liftoff on

the launch pad!

Then this mighty

rockets that deliver

precious cargo to

space are being

disposed of and they

fall back into the ocean

uncontrollably. Each

time you deliver

something to space,

you need a big space

agency like NASA or

ESA with big

contractors like Boeing

and Airbus to take

your cargo and put it

on top of a giant brand

new unused rocket

that will work for several minutes and then all these millions

will be thrown away in the sea contributing to the

environmental impact we have on our planet! We use our

multi-million dollar rockets, a state of the art machines that

has been created and perfected by the greatest human

minds, only once! No wonder that it is expensive to go to

space! Imagine you had to buy a brand new Boeing 747 each

time you needed to cross the Atlantic Ocean! Not so

financially viable, eh?! Very few people would travel with

airplanes then.

Image 10: Boeing 747 – one of the largest aircrafts produced by man

Well, this is about to change in the future, of course. What

if I tell you that the future is now! We already know how to

launch successfully a rocket and we have mastered it to the

point where astronauts visit and stay in the Space Station on

a regular basis. Rocket launches are still exciting events

today, but for a

little bit

different

reasons than

the rocket

launches in the

60s when every

other rocket

made

spectacular

fireworks show

in a try-and-see-

what-will-happen attempt to go to space. Today we must

learn how to land our rockets back to Earth and I don’t mean

leaving them to just crash somewhere. I mean a controlled

landing of a rocket back on a pre-determined place on the

ground where it can be re-fueled and sent to space again in

a few hours! This might sound like a science fiction now, but

it sure doesn’t to Elon Musk – the founder of Space

Exploration Technologies (SpaceX), a private

entrepreneurial rocket company headquartered in

Hawthorne, California, that develops their rocket Falcon 9

v1.1 to be the first rapidly reusable rocket in the world!

Image 8: lots of money

Image 9: The Soyuz rocket on the Launch pad in Baikonur

Image 11: Rocket failures are relatively rare nowadays

4

Image 12: Elon Musk – the founder of SpaceX and Tesla Motors

Mr. Musk is a bold visionary who concluded that if we are

ever to become a spacefaring civilization, we need to have a

rapid and inexpensive access to space! A SpaceX Falcon 9

rocket costs around 60 million dollars to launch and it is one

of the cheaper alternatives out there. What is fascinating,

and this might be counter-intuitive to many, is that most of

the cost to build a Falcon 9 (and any other rocket for that

matter) is going for the construction of the rocket itself and

the fuel for the launch is only 2% of the total cost! So, if we

find a way to bring back our precious rocket from space and

reuse it, we can drop down the cost of space flight 10 times

at least (an order of magnitude)!

NASA reached a similar conclusion to Elon when they built

the Space Shuttle, but it was an incredibly complex machine,

very expensive and it wasn’t really rapidly reusable. Instead,

it needed months of refurbishing after each return to Earth

in order to get it to the state it needed to be in order to fly

again to space. Falcon 9, on the other hand, is a conventional

rocket (at least to the extent that it doesn’t have large wings

like the Shuttle), but that is only on a first sight.

Image 13: The Space Shuttle

Imagine you are an astronaut about to travel with the

Dragon Crewed Spacecraft on top of the Falcon 9 Reusable

(F9R) and it’s launch day today on Cape Canaveral!

Image 14: The Dragon crewed spacecraft and Falcon 9R

You had a breakfast, you suited up in your space suit, and

you took the elevator to the top of the rocket and God, how

big the rocket looks from up here – you are about 60 meter

above the ground, next to the hatch of the Dragon capsule

and you can see kilometers away into the distance. You (and

your 6 crewmates) are about to go to the Space Station and

you will see Earth from the Cupola!

Image 15: Astronauts before departure to the ISS and a look from the Cupola on the ISS

You have paid only 1 million dollars to be on this seat, you

have trained for several years and it’s all about to culminate

now! You have the flight control panels touch screens in

front of you switched on, you make sure all the

communication systems are working, you are doing

communication checks and you listen to some rock’n’roll

music while you sit back and relax, letting the ground team

do their job. Everything has to be checked before the launch

of this state-of-the-art rocket.

Image 16: The interior of the Dragon crewed capsule (left) and the Soyuz spacecraft (right)

Falcon 9 v1.1 is a two-stage launch vehicle (rockets need to

be constructed of 2 or 3 stages to go to space) that stands

about 69 meters tall

with a liftoff mass of

about 506 tons when

flying in its F9R version

with a re-usable first

stage. Falcon 9R Stage 1

is about 43m tall and

3.7m in diameter and

contains an oxidizer tank

located above a fuel

tank (rockets need

oxygen like the one that

we breathe in the air,

but in liquid form and a

lot of kerosene as a

propellant). The oxidizer Image 17: Falcon 9R schematic

5

tank utilizes a monocoque structure and is filled with Liquid

Oxygen oxidizer (LOX). The fuel tank features a

stringer/ring-frame for additional strength to the vehicle

and is filled with Rocket Propellant-1 (RP-1) as fuel which is

highly refined Kerosene. The walls of the first stage are

made from aluminum lithium alloy welded together through

special techniques for maximum strength. The LOX feedline

is routed through the center of the fuel tank to supply

oxidizer to the engines. The overall propellant mass in the

first stage is 385 tons! The fueling process begins about

three hours before launch – RP-1 kerosene propellant first,

then the liquid oxygen. The plume that comes out of the

rocket during the countdown is gaseous oxygen being

vented from the tanks, which is why the liquid oxygen is

topped off throughout the countdown.

A few minutes before liftoff it actually starts to sink in that

you are actually going to space now! Terminal countdown

begins at T-10 minutes and all systems are autonomous at

this time. Eight minutes before liftoff the Dragon capsule

goes to internal power and 5 minutes before liftoff the

rocket is standing by itself on the launch pad as the strong

back next to it retracts. Then you can feel the enormous

power of the engines underneath you at T-0.

Falcon 9R sports 9 Merlin 1D engines at its bottom that are

arranged in an “octaweb” configuration (Image 19). Eight

engines are arranged in a circle around a single engine at the

center that is installed slightly lower with its nozzle

protruding the others.

Image 19: Octaweb Merlin 1D engines configuration

The Merlin 1D engine is a gas generator engine. What does

this mean? It produces large volumes of relatively cool gas

that is used to power turbo pumps. The gas generator

exhaust pipes of the individual engines installed on the

perimeter of the first stage are arranged toward the inboard

direction and their flow passes through the gap between the

center and other engines.

With its nine first-stage Merlin

engines clustered together, Falcon

9 can sustain up to two engine

shutdowns during flight and still

successfully complete its mission.

This new design eliminates a lot of

structure that needs to be installed

to carry loads from the engines to

the Stage 1 skin. The original

configuration of the 9 Merlin

engines was a tic-tac-toe and needed a lot of load-

transferring structures, adding to the overall mass of the

rocket.

Image 21: The original and octaweb configurations of Falcon 9’s engines

All nine engines are ignited about three seconds before

launch and reach operational conditions and liftoff thrust of

654 Kilonewtons (enough to balance about 66,700kg) each

giving Falcon 9 a total liftoff thrust of 5,900kN (600,200kg).

The engine’s combustion chamber operates at a high

pressure of 97 bars to generate these enormous trusts that

Image 18: Falcon 9 and 9R launches

Image 20: A LOX and RP-1 turbo pumps with the turbine at the bottom

6

lift the rocket off the ground! These pressures are around 40

times higher than the pressures in your automobile tyres!!

If you are interested in the construction of a Merlin 9 engine,

here is a schematic that explains it in brief (Image 22).

You can feel the enormous power during liftoff and ascent

through the atmosphere while you sit comfortably in your

seat inside the capsule. Seventy seconds after liftoff Falcon

9 reaches supersonic speed and shortly after that the rocket

passes through the area of maximum aerodynamic pressure

– max Q. This is the point when the mechanical stress on the

rocket is strongest due to a combination of the rocket’s high

velocity and the resistance created by the Earth’s

atmosphere. During ascent the rocket’s engines are

monitored constantly and computers can shut down any

engine at any time to prevent a disaster (or as they put it

more scientifically – RUD – rapid unplanned disassembly).

Falcon 9 is a safe rocket with a perfect track record (and I am

sure you know that when you trusted SpaceX to take you to

orbit), but rest assured that in the case of an unplanned

shutdown of an engine, the flight computer would re-plan

the ascent trajectory with the remaining engines by

extending their burn. The first stage is equipped with

Reaction Control System that uses nitrogen for three-axis

control of the rocket.

You are already 2 minutes and 40 seconds into the flight on

an altitude of 80 kilometers when the first stage engines are

shut down, an event known as main engine cutoff – MECO.

At this point you are already traveling at 10 times the speed

of sound! (a speed of Mach 10 - this is more than 3,400

meters per second!) The first stage is separated and you

continue your ride to the Space Station with the single

Merlin MVac engine of the second stage. We will leave you

to enjoy your ride and have a safe trip, but we will look at

something very interesting that is about to happen with the

first stage after its separation.

Immediately after the first stage separates from the Falcon,

it starts a very unusual journey back to Earth to a pre-

determined landing site with the idea to be reused many

times afterwards. This is the most expensive part of the

Falcon rocket and if we manage to fly it more than once, it

will reduce the cost of space flight with two orders of

magnitude. So, let’s see what happens during these

extraordinary first attempts of SpaceX to bring back

successfully the first stage to Earth.

Image 23: A schematic of a Falcon 9R landing procedure

Immediately after detachment, the first stage embarks on a

trajectory with a maneuver that will lead it away from the

plumes of the second stage that fires above it. It does that

with an attitude control system that uses cold gas nitrogen

thrusters on the top side section that keep it oriented on the

right path. Remember that the stage’s speed at this point is

around 10 times the speed of sound. This trajectory will

ultimately lead it to an altitude of 140 km oriented with its

nine Merlin engines pointing to Earth (Image 23).

Around 4 minutes and 30 seconds into the mission, the first

stage re-lights a subset of its engines for a boost-back

maneuver (Image 24) that slows the stage down and

controls its downrange travel distance, beginning to target

the planned landing site – either on land or in the ocean. The

duration of the boost-back burn depends on the target

landing site and is also driven by propellant availability for

the return which varies depending on payload mass and

insertion orbit.

Image 24: Falcon 9R’s Stage 1 boost back burn

Image 22: The structure and components of a Merlin 1D engine

7 Heading back into the dense layers of the atmosphere, the

first stage completes its supersonic retro propulsion burn

using three engines that are fired for about 20 seconds

starting at an altitude of 70 Kilometers (Image 25). This burn

in combination with drag in the atmosphere slows the first

stage down from 1,300m/s to about 250m/s.

Image 25: Falcon 9R’s Stage 1 re-entry burn at 70km altitude

The first stage aft section has been outfitted with shielding

material to be able to withstand the re-entry environment

and during atmospheric flight, the stage can maintain an

engine-forward position by its low center of gravity caused

by the heavy engine compartment in the aft.

At the beginning of re-entry the booster expands its four grid

fins for orientation control (Image 26), especially during the

periods of flight when the engines are not running. These

four grid fins are launched in a position stowed against the

uppermost section of the booster near the interstage.

Image 26: Falcon 9R’s grid fins used for landing accuracy

They can be controlled individually to allow for complex

guidance during the atmospheric flight without active

propulsion of the booster back to Earth. Grid fins perform

well in all velocity ranges including supersonic and subsonic

speeds (more than 1700m/s and less than 270m/s) with the

exception of the transonic regime (between 270 and

410m/s) due to the shock wave enveloping the grid. These

properties make them ideally suitable for the Falcon 9 first

stage. The addition of the grid fins to the Falcon 9 rocket

improved landing accuracy to the level of landing the first

stage to a mobile drone ship in the sea.

Image 27: Falcon 9R approaching the landing site in the sea

The Autonomous Spaceport Drone Ship (ASDS) (Image 28)

is a floating landing platform that measures 91 meters by 52

meters.

Image 28: The Autonomous Spaceport Drone Ship (ASDS) named “Just Read The Instructions”

It uses GPS data to keep its assigned position with an

impressive accuracy of only three meters. This high level of

accuracy is essential since the landing legs of the first stage

have a span of 18 meters, leaving just over 30 meters for GPS

errors between the two crafts, sea swell and errors by the

first stage.

The ASDS is outfitted with a water deluge system that

dumps water onto the deck to protect it from the heat of

the engine of the arriving booster. There are numerous

attachment fixtures on the deck structure that allow the

securing of the first stage after the landing on the platform.

Image 29: The ASDS

Homing in on its landing spot, the first stage ignites its center

engine to begin slowing down to a landing speed of just

about two meters per second and make the final cross-track

and range adjustments to land on the platform (Image 30).

8 Ten seconds into the landing burn, the four landing legs are

deployed to put the stage into its final landing configuration

with touchdown just a few seconds later.

Image 30: Falcon 9R’s Stage 1 a second before landing on the ASDS in the sea

Wait a second – landing legs on a rocket? (Image 31) Yes!

Falcon 9 Stage 1 has four deployable landing legs that are

tucked right next to body of the rocket and in the final stages

of landing they are

spread and locked into

landing position to

support the 20 tons

stage on landing. Each

landing leg weighs just

above 500 kg and is

protected by a

special paint.

We live in extraordinary times! You can use the power of

the sun and electricity to drive an electric automobile with

Tesla Motors or the power of the sun, solar panels and

battery storage capacity to power your home entirely on sun

power and completely cut yourself off the electric grid. We

are also witnessing the first steps of the human civilization

to become a space faring civilization the same way like a

hundred years ago we discovered that we can actually

invent flying machines! In a few decades it will be something

usual to go to a spaceport, pay your ticket to lower Earth

orbit or the Moon and go for a weekend holiday or to work

“upstairs”. When you are there, you will see the beauty of

our spaceship Earth – the only place that we have in the

Cosmos! This is a huge perspective changer! You will call a

relative of yours who lives on Mars for a few years now and

you will tell him how beautiful Earth is. All this will become

possible with the invention of reusable rockets such as

Falcon 9. Others will follow in the space sector as in the

energy consumption sector with electric automobiles and

the energy production sector with solar power and storage.

It is high time to start living like intelligent human race, not

like pigs!

A few centuries from now when our home will be the whole

solar system, we will look back and remember these first

puny attempts to get up from the cradle and leave Earth’s

atmosphere and reach to the stars. It is a story for the

books…

Tihomir Dimitrov

The Human Adventures in Space Exploration

www.humansinspace.org

Image 32: SpaceX Landing Complex 1 – the first rocket landing facility in the world

Image 31: Falcon 9R’s landing legs