Trajectory Reverse Engineering 

A strategy for transferring spacecraft trajectories between flight mechanics tools, called Trajectory Reverse Engineering (TRE), has been developed[1]. This innovative technique has been designed to be generic, enabling its application between any pair of tools, and to be resilient to the differences found in the dynamical and numerical models unique to each tool. The TRE technique was developed as part of the NESC study, Flight Mechanics Analysis Tools Interoperability and Component Sharing, to develop interfaces to support interoperability between several of NASA’s institutional flight mechanics tools.  

The development of space missions involves multiple design tools, requiring the transfer of trajectories between them—a task that demands a large amount of trajectory data such as frames, states, state and time parametrizations, and dynamical and numerical models. This is a tedious and time-consuming task that is not always effective, particularly on complex dynamics where small variations in the models can cause trajectories to diverge in the reconstruction process.   

The TRE strategy is a trajectory-sharing process that is agnostic to the models used and performed through a common object: the spacecraft and planet kernels (SPK), developed at JPL Navigation and Ancillary Information Facility. The use of this common object aims to lay the groundwork for a global flight mechanics tool interoperability system (Figure 1). 

An SPK file serves as a container object, representing a trajectory as a 6D invariant structure in phase-space, agnostic to gravitational environments, fidelity models, or numerical representation of the system. A judicious kernel scan is used to recover the trajectory in any new tool, with the minimum (or no) information from the generating source. Impulsive maneuvers can be extracted in the form of velocity discontinuities, finite burns can be detected as variations on the energy of the system, and natural bodies conforming the trajectory universe can be directly read from the kernel.  

States or control points are found at predetermined time intervals or strategic points along the trajectory (e.g., periapsis, apoapsis, flybys closest approach), which are then used to reconstruct the trajectory timeline. The trajectory can be propagated forward in time using the selected set of control points. Due to the discrepancy between tool models, small or large discontinuities might appear between the integrated legs, which can be smoothed by the implementation of a multiple-shooting algorithm (Figure 2).  

The TRE strategy was successfully implemented for Monte and Copernicus in the form of Python scripts (examples of reconstructed trajectories from SPK for each of these tools are shown in Figure 3). Through an optional user input file, a user can configure their specific problem. User-defined constraints are also possible, but their implementation would depend on the specific tool. The benefits of this effort include cost reduction through the sharing of capabilities, acceleration of the turnaround process involving various analysis tools at different stages of mission development, improved design solutions through multi-tool mission designs, and a reduction in development redundancy. 

Reference: 

1. Restrepo, R. L., “Trajectory Reverse Engineering: A General Strategy for Transferring Trajectories Between Flight Mechanics Tools” AAS 23-312, January 2023. 

For information, contact Heather Koehler heather.koehler@nasa.gov and Ricardo L. Restrepo ricardo.l.restrepo@jpl.nasa.gov. 

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Meagan Chappell

NASA’s Hubble Pauses Science Due to Gyro Issue

NASA is working to resume science operations of the agency’s Hubble Space Telescope after it entered safe mode April 23 due to an ongoing gyroscope (gyro) issue. Hubble’s instruments are stable, and the telescope is in good health.

The telescope automatically entered safe mode when one of its three gyroscopes gave faulty readings. The gyros measure the telescope’s turn rates and are part of the system that determines which direction the telescope is pointed. While in safe mode, science operations are suspended, and the telescope waits for new directions from the ground.

This particular gyro caused Hubble to enter safe mode in November after returning similar faulty readings. The team is currently working to identify potential solutions. If necessary, the spacecraft can be re-configured to operate with only one gyro, with the other remaining gyro placed in reserve . The spacecraft had six new gyros installed during the fifth and final space shuttle servicing mission in 2009. To date, three of those gyros remain operational, including the gyro currently experiencing fluctuations. Hubble uses three gyros to maximize efficiency, but could continue to make science observations with only one gyro if required.

NASA anticipates Hubble will continue making groundbreaking discoveries, working with other observatories, such as the agency’s James Webb Space Telescope, throughout this decade and possibly into the next.

Launched in 1990, Hubble has been observing the universe for more than three decades and recently celebrated its 34th anniversary. Read more about some of Hubble’s greatest scientific discoveries and visit nasa.gov/hubble for updates.

Media Contact:

Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, MD
claire.andreoli@nasa.gov

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NASA’s Commercial Partners Deliver Cargo, Crew for Station Science

NASA partners with commercial companies to provide safe, reliable, and cost-effective transportation of cargo and crew members to and from the International Space Station. A platform for long-duration research in microgravity, the station has operated continuously for more than 23 years, its crew members conducting a broad range of technology demonstrations and thousands of experiments in many scientific fields.

Human Transportation

NASA’s Commercial Crew Program provides systems capable of carrying astronauts to low Earth orbit and the space station through industry partners who design, build, test, and operate these systems. Crew members providing hands-on operation of scientific research is one of the unique advantages of the orbiting laboratory. Human operators monitor events on Earth in real time, swap out experiment samples, observe results firsthand, assess when conditions are favorable for data collection, and troubleshoot and otherwise manage and maintain scientific activities. Crew members also pack experiment samples to return to the ground for detailed analysis.

NASA commercial partner Boeing is launching NASA astronauts Butch Wilmore and Suni Williams on a Crew Flight Test of its Starliner spacecraft in May 2024. The spacecraft launches to the space station on a United Launch Alliance Atlas V rocket from Cape Canaveral Space Force Station, Florida. This mission paves the way for NASA to certify the Starliner spacecraft for long-duration rotation missions to the space station.

SpaceX, another commercial partner, conducted an uncrewed Demo-1 flight in March 2019, and in May 2020, the Demo-2 flight carried NASA astronauts Robert Behnken and Douglas Hurley to the space station. The first operational mission, Crew-1, launched in November 2020. Since then, SpaceX has regularly sent crews to the orbiting laboratory for scientific missions. The Dragon spacecraft launches on the company’s Falcon 9 rocket from NASA’s Kennedy Space Center in Florida.

NASA’s commercial crew flights have significantly increased the amount of crew time available for research and expanded the potential for commercial use of the orbiting laboratory. More crew members mean more time for scientific research and technology demonstrations, and ultimately, more scientific results. To date, results generated by space station research range from improvements in the development of pharmaceuticals to better disaster response, improved materials manufacturing, advances in robotics, bioprinting human tissue, and more.

By enabling regular rotation of crew members, commercial crew flights also contribute to research on how long-duration missions affect human health, helping to prepare for exploration missions to the Moon and Mars.

Cargo Resupply

Through NASA’s Commercial Resupply Services program, partners SpaceX and Northrop Grumman fly cargo to the space station on rockets and spacecraft the companies developed.

Northrop Grumman transports scientific investigations and cargo on its Cygnus spacecraft. The company’s first resupply mission launched in 2013 and it had reached 20 missions by January 2024. When a Cygnus departs from the space station, it disposes of several thousand pounds of waste that burn up during re-entry into Earth’s atmosphere.

Departing Cygnus spacecraft also provide safe platforms to perform research that could create hazards if conducted on the space station, such as the Spacecraft Fire Safety Experiments (Saffire). This eight-year series of investigations studied flame growth and material flammability in space. The experiments were ignited in the cargo vehicles after their departure from the station and before re-entry to Earth, avoiding potential risk to the space station and its crew.

SpaceX launched its first Dragon cargo mission in October 2012 and by March 2024, had sent 30 commercial resupply services missions to the space station. Dragon is a reusable spacecraft that also returns samples from scientific investigations conducted on the space station. Beginning in 2021, these return flights started splashing down near Kennedy rather than in the Pacific Ocean. This capability allows scientists quick access to samples to make additional observations and analyses before the effects of gravity fully kick back in. Many researchers also conduct more in-depth analysis later in their home labs.

NASA also is working with Sierra Space to develop the Dream Chaser spacecraft to transport cargo to and from the space station. The reusable, winged spacecraft is designed to use commercial runways and its cargo is subject to reduced gravitational forces on the return flight. Sierra Space conducted an autonomous atmospheric test flight in 2017.

These commercial partnerships build a strong American commercial space industry, as NASA focuses on developing the next generation of rockets and spacecraft for deep space missions and to put the first woman and first person of color on the Moon.

Melissa Gaskill
International Space Station Research Communications Team
NASA’s Johnson Space Center

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Ana Guzman