NASA has released information regarding the U.S. space agency’s payloads that will launch on the Air Force’s STP-2 (Space Test Program -2) mission on SpaceX’s Falcon Heavy rocket later this month.

Meanwhile, in Florida, Landing Zone -1 (LZ-1) has been cleared to return to normal operations following the Crew Dragon anomaly on 20 April, paving the way for the site’s use as one of the landing locations for one of Falcon Heavy’s side boosters.

The third Falcon Heavy mission is set to launch No Earlier Than (NET) Monday, 24 June 2019 from LC-39A at the Kennedy Space Center, FL. The day’s launch window opens at 23:30 EDT and will mark the Falcon Heavy’s first night launch.



Falcon Heavy payloads from NASA:

In all, four NASA payloads will ride-share their way to orbit aboard the Falcon Heavy during the STP-2 mission, managed by the U.S. Air Force Space and Missile Systems Center.

The NASA payloads, four of the 24 total payloads on this mission, are designed to test a variety of technologies that the agency hopes will one day improve upon current spaceflight technologies.

The NASA payloads are: the Deep Space Atomic Clock, the Green Propellant Infusion Mission, the Space Environment Testbeds, and the Enhanced Tandem Beacon Experiment.

Deep Space Atomic Clock:

This experiment will be the world’s first ion-based atomic clock to be flown in space with the goal of dramatically improving space-based navigation via timekeeping pieces 50 times more stable than the GPS atomic clock.

To this end, the Deep Space Atomic Clock (DSAC) is built to maintain timekeeping accuracy to within one second over 9 million years.

First and foremost, this experiment seeks to demonstrate an atomic clock’s operation in Low Earth Orbit to validate the functionality of the device as well as test its capabilities for future applications on deep space missions.

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While it might seem trivial that a spacecraft carry an atomic clock for navigation purposes, the application’s benefit is made clear when its potential streamlining of navigation services are compared with current deep space probe practices.

Presently, pinpointing a spacecraft’s position in space and determining its precise trajectory involves sending a radio navigation beam from Earth toward the spacecraft, bouncing that radio wave off the spacecraft, and then measuring how long it takes the beam to return to Earth – a process known as radio echo.

From that transit time and return direction, scientists can calculate a probe’s trajectory, distance, and velocity compared to Earth and therefore gain an understanding of its trajectory through the solar system.

In this manner, tracking a spacecraft through the solar system is a fundamental problem of tracking time.

Enter the Deep Space Atomic Clock (DSAC).

Developed over the last 20 years by engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, the DSAC is a miniature, ultra-precise, mercury-ion atomic clock that is orders of magnitude more stable than the best navigation clocks in use today.

By implementing this technology on deep space probes, it would effectively cut the process of navigating a spacecraft in half by eliminating today’s radio echo method of tracking.

Instead, the DSAC would send an ultra-precise time signal directly to Earth from which the exact same data garnered by radio echo could be discerned.

This one way tracking with high precision accuracy would provide a more flexible way of tracking a spacecraft and navigating through the solar system while also shifting to a more efficient use of the Deep Space Network – which would be freed up from radio echo tracking of one spacecraft at a time to tracking multiple spacecraft at the same time.

Moreover, it would enable autonomous, real-time spacecraft navigation of our deep space probes and would – for human mission implementation – be able to deliver a spacecraft to a more precise landing site with less uncertainty.

Following launch, the DSAC will be powered up in August with preliminary results returned to Earth in the fall.

In total, the technology demonstration carries three main objectives: 1. Demonstrate performance of the clock in a long-term LEO environment; 2. Demonstrate that the clock operates for a year in space uninterrupted; 3. Perform DSAC analogue experiment (process tracking data that mimics deep space navigation, like a Mars spacecraft).

Beyond its navigation prospects for deep space probes, DSAC could also enable the creation of GPS networks around moons and other planets in our solar system, specifically Earth’s moon and Mars.

In this manner, non-Earth GPS networks would work the same as the current GPS constellation, with moon- and planet-wide orbital networks of satellites containing DSACs transmitting radio signals down to receivers – radio signals that would then be converted into precise time and location information for users.

While this is just a technology demonstrator at the moment, NASA said the possibility of including DSAC on the next Mars telecom satellite in support of NASA’s upcoming Mars Sample Return mission is a possibility – though an exact timeframe for such a satellite is currently unknown.

Green Propellant Infusion Mission:

The Green Propellant Infusion Mission (GPIM) will provide an in-space test for a new green propellant that has been developed over the last two decades by the Air Force Research Laboratory at Edwards Air Force Base, CA.

The propellant in question, named AF-M315E, is an “innovative, low-toxicity propellant” that will provide a green and safer alternative to today’s highly toxic hydrazine fuel used for spacecraft in-flight propulsion.

Good things come in mini-fridge-sized packages. The Green Propellant Infusion Mission will test a low toxicity propellant in space for the first time. This technology could lengthen mission durations by using less propellant. Go green — in space: https://t.co/furecJkZz9 pic.twitter.com/RJa4XN5QNQ — NASA (@NASA) May 21, 2019

According to NASA, “NASA and its partners always strive to maintain the strictest safety standards for storage, transport and use of rocket propellants. While all rocket fuels can be dangerous to handle without the proper safety precautions, AF-M315E has significantly reduced toxicity levels compared to hydrazine, making it easier and safer to store and handle.”

AF-M315E itself is a Hydroxyl Ammonium Nitrate fuel/oxidizer blend that costs roughly $500,000 less to process, handle, transport, and load into spacecraft than hydrazine.

Moreover, it can be transported commercially in U.S. Department of Transportation approved containers, can be loaded into satellites and probes before they ship to their launch locations, and can be loaded by personnel wearing gloves instead of full, pressurized SCAPE (Self-Contained Atmospheric Protective Ensemble) suits.

AF-M315E is also more dense than traditional hydrazine – meaning the same amount of AF-M315E creates more specific impulse (thrust delivered per given quantity of fuel) than the same amount of hydrazine.

Moreover, AF-M315E’s crystalline fuel structure undergoes a glass transition at cold temperatures but does not freeze as hydrazine does at the same temperatures.

This is important because in a glass transition phase, AF-M315E solidifies but does not expand – meaning mission engineers do not have to keep AF-M315E from solidifying in order to prevent the spacecraft’s fuel lines from rupturing as they do with hydrazine – because when hydrazine freezes, it expands and ruptures fuel lines.

To this end, use of the AF-M315E green propellant would free up electricity normally used to keep hydrazine heated above freezing limits to power other elements of the mission and scientific objectives.

The new propellant will be tested on a small spacecraft that will use five 1 Newton thrusters to perform various orbital operations – including deorbit, with the goal of re-entering the experiment into the atmosphere within a couple of weeks.

But perhaps an even greater demonstration of this fuel’s prospect is the fact that numerous missions are already in line to use it for in-space maneuvering pending a successful outcome of this technology demonstration.

Space Environment Testbeds:

The Space Environment Testbeds (SET) experiment will fly and operate inside the slot region between the two doughnut-shaped regions of the Van Allen radiation belts around Earth.

While the Van Allen Radiation Storm Belt probe mission, a set of two identical spacecraft that have spent the last seven years investigating and characterizing the Van Allen radiation belts, have done a great job of exploring the inner and outer belts, they were not designed nor have they greatly explored the slot region.

This is where the SET experiment will fly, with a specific mission task of characterizing the harsh space environment near Earth and how it affects spacecraft in their instruments.

Dr. Nicola Fox, director of the Heliophysics Division of NASA’s Science Mission Directorate, said that scientists are aware of the effects of space weather and radiation on satellites, and ensuring that we build robust satellites is key.

But so is making sure we don’t build over-robust satellites. As Dr. Fox related, “We don’t want to put a battleship into orbit when a dinghy will do.”

The types of space weather and radiation of most concern for space probes are energetic particles that can cause computer and hardware damage – and these particles are exactly what the Van Allen radiation belts trap.

Thus, while protecting spacecraft against radiation is a key to spacecraft functionality, so too is understanding the best possible places to put them in orbit around Earth.

And one of these idea locations might be the slot region between the two Van Allen radiation belts as this region has less radiation than other parts of near-Earth space.

The Van Allen radiation belts themselves trap protons and electrons, the exact energetic particles which spacecraft designers have to protect against.

But galactic cosmic ray protons and heavy ions also play a part in spacecraft design and protection – and these types of protons and heavy ions can also be erupted from the Sun in major coronal mass ejections and solar flares.

Thus, part of the SET mission is designed to characterize the environment of the slot region and determine the proportion of energetic particles trapped there and whether they emanated from the Sun or come from sources outside of the Sun’s heliosphere.

This information will greatly help engineers design spacecraft that can withstand this environment while not over building them by adding unnecessary weight and systems that aren’t needed.

Enhanced Tandem Beacon Experiment:

Enhanced Tandem Beacon Experiment (E-TBEx) explores bubbles in the electrically-charged layers of the upper atmosphere which can disrupt key communications and GPS signals.

Two tiny satellites are headed to space on the same launch. 🛰🛰 E-TBEx will study how signals like GPS are distorted as they pass through Earth's upper atmosphere on their way to the ground — knowledge that could help us avoid communications problems: https://t.co/CSfvqqEkf3 pic.twitter.com/0E83voLTAi — NASA Sun & Space (@NASASun) June 10, 2019

These bubbles appear in unpredictable fashion and are difficult to characterize from ground-based observations; but flying E-TBEx may shed light on their formation and evolution.

E-TBEx will use two CubeSats that will emit signals at various frequencies, signals then received at ground stations that can measure how the signals at various frequencies are disrupted by these atmospheric bubbles.

The CubeSats will work in conjunction with NOAA’s (National Oceanic and Atmospheric Administration) COSMIC-2 mission – a six satellite constellation that will carry beacons similar to those used on the E-TBEx CubeStats – thus enabling multiple angle cross examination of the same atmospheric bubble at the same time from eight spacecraft in Low Earth Orbit.

Specifically, E-TBEx is designed to study the formation of these bubbles in the ionosphere of Earth’s atmosphere.

These bubbles form based on the relationship between incoming space-weather from the Sun and outgoing ground-based weather in Earth’s atmosphere – though the extent of this interaction and exactly how it creates these bubbles is largely unknown.

According to NASA, “Factors from near Earth’s surface, like weather, and changing conditions in space called space weather can influence the winds and the electric and magnetic fields to push around the gases in the ionosphere – making it hard to predict what its state will be at any given time.

“In particular, structured, less-dense bubbles of plasma form within pockets of denser plasma near Earth’s magnetic equator, then shift and dissipate, influenced by a poorly understood mix of these factors.”

To this end, “E-TBEx [will study] the evolution and impacts of the ionospheric bubbles on communications signals by sending signals with precise characteristics from the CubeSats in low-Earth orbit to receiving stations on the ground – right through the ionosphere, and, sometimes, through these structured bubbles of plasma.

“Ultimately, this research could help inform strategies for making communications and navigation more robust, allowing users – including the military and commercial aircraft operators – to shift to a different frequency, change information-encoding techniques, or delay key communications if an ionospheric bubble is spotted.”

Falcon Heavy launch processing; LZ-1 ready to support side booster landing:

While final payload preparations continue, the Falcon Heavy itself is coming together inside the Horizontal Integration Facility (HIF) outside the pad perimeter gate of LC-39A.

Inside the HIF, the two side boosters, which were previously used on the last Falcon Heavy flight in April, are being joined to the center booster.

The center booster is brand new, and while not originally anticipated to serve as a replacement for the previous Falcon Heavy center booster is now acting as such after the Arabsat 6A Falcon Heavy center booster was destroyed in rough seas after landing on the ASDS Of Course I Still Love You drone ship.

Final integration of the Falcon Heavy stack will include mating of the second stage to the top of the triple booster base, after which the entire assembly will be lifted up and then lowered onto the Transporter/Erector.

The payload-less Falcon Heavy will then make a short journey to the launch pad, where it will be erected vertical and put through a Static Fire test – expected early next week at present.

Static Fire will culminate with a 3 to 7 second firing of all 27 Merlin 1D engines on the base of the Falcon Heavy.

As with the previous launch campaign, all 27 engines are expected to be ignited simultaneously during Static Fire – imparting 5.1 million lb of thrust into LC-39A.

If the Static Fire goes well and reveals no issues, Falcon Heavy is expected to proceed toward launch on the STP-2 mission on Monday, 24 June 2019 during a launch window that opens at 23:30 EDT (03:30 UTC on 25 June).

Following launch, the two side boosters will flip around and perform synchronized, simultaneous landings at Landings Zones -1 and -2 (LZ-1 and LZ-2) at the Cape Canaveral Air Force Station.

Less than a minute after side booster separation, the center booster will separate and – for the first time on a Falcon Heavy – will also flip around and boost itself back to the Cape.

Because SpaceX only has two landing pads on land at Cape Canaveral, the center booster for the STP-2 Falcon Heavy will land approximately 17 km offshore on the ASDS drone ship Of Course I Still Love You.

The quasi-RTLS (Return To Launch Site) landing of the center booster will mark the first time all three boosters will return to the Cape for landing.

In terms of the two side boosters, LZ-1 has been cleared to return to normal operations following the test anomaly of the Crew Dragon capsule on 20 April.

The clean up, decontamination, and investigation process that has occurred at LZ-1 in the last two months was a critical part of the Crew Dragon investigation.

LZ-1 has been closed since the accident to all non-incident recovery operations.

In early May, SpaceX moved a planned LZ-1 booster landing to the ASDS Of Course I Still Love You that was positioned 12 km offshore during the CRS-17 launch.

The option to move a side booster landing for Falcon Heavy to the ASDS was not possible given Of Course I Still Love You is needed for the center booster landing.

The return to operation of LZ-1 now paves the way for it to be used for the Falcon Heavy mission later this month and for all three boosters to be recovered for reuse.

There is still work to be done at LZ-1, however, to prepare it for landing operations.

Those operations will take place over the following week.