Day in the Life Series: Hot Fire and Cold Flow Wrap

Here’s a recap of every “day in the life” post on hot fires and cold flows to date.

Up next, another interview from the bunker. Stay tuned.

A Day in the Life of a Hot Fire

Part One: Morning prep and checklists

Part Two: Caravan

Part Three: Bunker and Test Stand

Part Four: Roles

Part Five: Hot Fire!

A Day in the Life of a Cold Flow

Part One: Roll out and tank fill

Part Two: Bottle Trailer

Part Three: Setup

Part Four: Cold Flow in Action!

A Day in the Life of a Hot Fire, Part Five: Ignition!

We’re at countdown to ignition!

After the crew has run through the stand setup, controls, and pressurization checklists (and a little lunch) they settle into the day’s series of hotfire objectives. Sometimes it can be a duration goal, a certain number of successful tests in a row with a new part, a certain pressure setting, fuel / LOX ratio change, or any combination of test objectives to further the test program.

The countdown for a hot fire is really the rundown of a detailed checklist that has been customized to test objectives. A majority of the checklist is nearly identical to many other tests, but there may be slight differences depending on the objective. There are built-in holds for tasks such as chilling down the pumps or waiting for the system to pressurize.

Regardless, as the checklist nears the bottom, the tension in the bunker starts to rise. Is it all correct? Did we set it up right? Are there any leaks? Will the new design work properly? All of those questions and more run through the team.

Then it’s time … “Engine run in three, two, armed! …”


Check out this video to experience what it’s like to prep and execute a hot fire:

A successful test results in beautiful images and beautiful data. 

This image (the thumbnail shot in the video above) was taken remotely by XCOR photographer and video engineer Mike Massee. It shows a brilliant plume overpowering the bright noon desert sky.

When a test series is concluded, the stand is disconnected, the bunker test equipment broken down and everything  is packed for the return. Our convoy makes its way back to the XCOR hangar, and on a good test day where everything goes smoothly, the crew typically returns between 3 and 4:30 pm. On later days it’s between 9 and 10pm.

After each test, an “after-action” meeting is held while all the information is still fresh in everyone’s heads. Each person present at the test is encouraged to bring up any issue, no matter how minor. There are no “dumb comments”, and all comments major and minor are captured on a “squawk list”. Suggested test stand or procedural changes are assigned to be completed before the next test. Data review is scheduled for the next day after everyone has had a chance to process and review the data on their own. And based on the data review, goals are set for the next test series.

Thanks for joining us for the “day in the life of a hot fire” series. Let us know what you think of it by connecting with us on Twitter or Facebook, or by emailing me at bryan [at] xcor [dot] com.


A Day in the Life of a Hot Fire, Part Four: Roles

So far this week, we have discussed the build-up to a hot fire.

Today, we’ll talk about the roles we play in the process.


In the bunker, a wall of video monitors gives the test crew excellent situational awareness. Cameras are placed to accommodate the specific test and points of interest. If needed, high speed and infrared cameras gather additional data. And on the radio, crew members are called-out by their positions.

Crew positions, roles and responsibilities for each hot fire include the following:

  • Control: Runs the control box and actually commands the rocket engine to fire.
  • DAQ: Runs the Data Acquisition Unit which records data from instruments on the stand. They are also responsible for displaying the data for instant review by the test crew after the test.
  • Red Team: This team directly interacts with the test stand while everyone else is inside the bunker. They return to the bunker during pressurization and during the actual hotfire.
  • Test Czar: This individual is in charge of the test and has the final say on go  / no-go conditions, and sets the test objectives and parameters. Acts as a safety net for the rest of the team, considering all possible risks before giving the green light.
  • Spotter: Acts as an additional safety check and spends most of the day seated on top of the bunker to keep an eye out for anyone approaching the test site. The spotter makes sure that the area down range of the rocket engine remains clear, and is only called-in just before the actual test.
  • Video: In charge of setting up and maintaining all the video feeds from the test site. The objective is to make sure to record all of the video during press, chill and hotfire.
  • Checklist: Acts as the pace setter for the test.  By reading  the checklist methodically and accurately they set the tempo for the test day. The checklist contains all of the commands for all of the other positions except the Test Czar.
  • Safety: The primary safety officer in charge of ensuring all  protocols are followed for the whole test. Safety may stop a test at anytime for any reason if they feel the crew or the uninvolved public are at risk.

Next up, the hot fire!

A Day in the Life of a Hot Fire, Part Three: Bunker and Test Stand

On Tuesday we told you about preparing to roll out for a hot fire. Wednesday was the journey to the test stand.

Today, what happens when we arrive …

Once we are at the test site, there is a flurry of activity. We attach the truss and fuselage to the test stand, a concrete slab rated for up to 80,000 lbf of thrust. It is a monster of a concrete pad, and contains various types of mounting brackets that can be used for a range of engine test stands.

Next to the test stand is our bunker. It is an old WWII ammunition storage bunker built by the US Navy Seabees for the Marine Corps, right around 1942. It is capable of withstanding the explosive energy of 435,000 pounds of TNT.


Shot atop the XCOR bunker, this photo shows the test stand in the foreground, and a bunker similar to ours in the background.

The bunker has very thick concrete walls and is covered by yards of earth. As a result it is cool in the summer and warm in the winter, with six inch-thick steel doors. It would make one heck of a man cave!


The interior of the XCOR bunker

We purposefully do not trick it out, because our philosophy is to have one culture at XCOR, not to have different mini-cultures grow up inside the company such as “the guys in the test bunker” or “those test stand fabricators” or “the composite team”. Everyone is one big team, and we all enjoy the simplicity of a day in the bunker!

As all of our test equipment is portable, very little remains out at the test bunker. When we arrive, the test stand is bolted to the test pad, cables are unreeled from the pad to the bunker, cameras are set up, and computer gear is electrically connected. Once everything is in position, gas and fluid cables for pressurization and valve control are attached and the “control room” inside the bunker goes live. The whole team is ready to ”get on checklist”.


XCOR senior shop mechanic Mike Laughlin checks a high-pressure hose fitting in preparation for a hotfire test.

Tomorrow we will show you the roles and responsibilities for the test, and you can decide what role you want to play!

A Day in the Life of a Hot Fire, Part Two: Caravan


The XCOR caravan makes its way past the “bone yard” for another hot fire.

Yesterday we went through initial morning activities that surround the day of a hot fire test, rolled out the flight weight fuselage and engine truss. We started to fuel LOX and kerosene around 7AM.

Cut to two hours later…

Around 9AM, after the kerosene and LOX fill is complete, and after running through check lists and various pre-rollout processes, we tow the engine test stand and truss out to the XCOR Test Bunker on the other side of the Mojave Air and Space Port.

The caravan of vehicles include the F-150 pickup truck with which we tow the test stand, a Hummer we use to tow the gas bottle trailer (a rolling stand filled with high pressure gases, such as helium and nitrogen, which we use for tests), and up to two more vehicles holding additional crew and equipment.

We cross the runways and taxiways of the Mojave Air and Space Port, past the “bone yard” of old aircraft, then into an area populated by numerous test sites for many of the space port tenants.

Because we travel within the boundaries of the airport and cross active taxiways and runways, we must have aviation radios and follow specific operational and communication procedures prior to departure, during movement, and upon leaving the active flight line. We pre-coordinate test activities with the local space port staff and first responders so they are fully aware of the planned activities and can, if they wish, monitor our activities in real time.

Tomorrow – What happens when we arrive at the test stand?

A Day in the Life of a Hot Fire, Part One: Morning prep and checklists


Brandon Litt (R) and Mike Valant (L) move the stand out from the XCOR hangar. 

Welcome to a day in the life of a hot fire. This is a journey through the experience of a test day where we work on a new, experimental rocket engine.

Due to the fact that the rocket engine is currently being proven, we maintain a very high level of safety protocols during each test. Once we’ve proven to ourselves that the engine is “maturing” we perform tests with our team members in closer proximity. In the future we will perform rocket engine firings with people onboard Lynx. But right now, we are showing you those first early engine firings when you need to expect the unexpected.

On the morning of a hot fire, the hangar is abuzz with activity. Members of the test team start to arrive around 6:30AM and begin to check and double check equipment and procedures. The team reviews what they will do, and everyone prepares for the day.

At around 7AM, the Lynx truss is rolled out of the hangar, and fueled-up with liquid oxygen (LOX) and kerosene. In the meantime, the test truck and vehicle convoy are loaded with all of the support equipment needed – tools, data acquisition, control box, safety equipment — in short, everything required to complete a test.

There are checklists for everything, including equipment inventory, stand setup, pressurization, hot fire, and shutdown. These checklists add safety and take the guesswork out of operations, and are a standard item in the world of aerospace testing and operations.

Tomorrow, take a trip out to the test stand and spend an afternoon with us.