In April 2007, the Defense Advanced Research Projects Agency showcased the capability to refuel a satellite in orbit by outfitting a spacecraft with a robotic arm, connecting it to another spacecraft, and transferring around 32 pounds of hydrazine into its fuel tank.

Fred Kennedy, who oversaw the project for DARPA, stated that the mission, called Orbital Express, achieved several technological milestones.

The U.S. mission not only highlighted the first-ever in-space refueling operation but also demonstrated the capability to employ tracking and imaging sensors to attach to a receiving satellite and do maintenance tasks like replacing a battery or flight computer.

Kennedy emphasized that autonomy was the key aspect during an interview with C4ISRNET on February 27. “We demonstrated an efficient method to approach a spacecraft closely and provide a range of servicing capabilities.”

Four months after its launch, the Air Force and NASA, DARPA’s mission partners, terminated the program.

The project lacked a clear mission application and was planned to support a space-based radar program that was terminated before Orbital Express began.

DARPA is accustomed to outcomes that are not surprising, as their projects frequently delve into cutting-edge technologies. Kennedy stated that he and his team stopped working on the project, expecting that the refueling and service concepts they showcased would reappear as agencies recognized their significance.

Kennedy stated that all of them believed there might be a brief pause. “No one anticipated that it would require 18 years to truly begin seeing the benefits of those accomplishments.”

According to a request from U.S. Space Command authorities to complete by the end of the decade, the Space Force is currently looking into the military benefits of including refueling capabilities in future space domain awareness satellites.

In 2020, the Space Force recognized servicing, mobility, and logistics as fundamental skills. The service has developed comprehensive requirements for the mission area. It formed a program office last year to coordinate development efforts and collaborate with companies to show refueling capabilities.

According to a request from U.S. Space Command authorities, the Space Force is currently looking into the military advantages of including refillable tanks on upcoming space domain awareness satellites before the end of the decade.

In 2020, the Space Force selected servicing, mobility, and logistics as essential skills. The service has developed comprehensive requirements for the mission area. It established a specialized program office last year to coordinate short- and long-term development initiatives and collaborate with enterprises to showcase refueling capabilities.

Current and former government and industry officials suggest that, due to pioneering flights like Orbital Express and initiatives from the commercial sector, the current difficulty is not primarily technological as momentum grows towards implementing these concepts. The Space Force’s objective is to establish a clear vision for the military’s use of on-orbit servicing and to play a role in funding and setting the standards that will influence the market in the short term.

Kennedy, the current leader of Dark Fission Space Systems, believes that the success of the company’s goal to advance nuclear thermal propulsion will rely heavily on the Space Force following through on its promises with tangible actions.

He stated that although words are pleasant, it is imperative that we start moving promptly. “I believe we have already waited 18 years excessively.”

Dynamic spatial operations
On-orbit servicing encompasses many capabilities designed to prolong a satellite’s lifespan or alter its mission performance. That may encompass refueling, maintenance, improvements, or supplying an additional propulsion source.

The Space Force began to focus more on on-orbit servicing a few years ago, but a significant shift occurred in 2022 when Space Command acknowledged that the satellites used to monitor the space environment were constrained by low fuel levels.

The purpose of the Geosynchronous Space Situational Awareness Program satellites is to act as a surveillance system in geosynchronous orbit, approximately 22,000 miles above Earth. The GSSAP satellites conduct rendezvous and proximity operations to approach and observe other spacecraft, especially those belonging to U.S. adversaries, in order to gather data on them.

Satellites, like other military space assets, were launched with a finite amount of fuel, which usually determines their operational lifespan. Lt. Gen. John Shaw, the former deputy chief of Space Command, noted that the limitation of not needing to maneuver may be suitable for a GPS or communication satellite, but it hinders the Space Force’s utilization of GSSAP and other space domain awareness systems.

Shaw informed C4ISRNET that Space Command was instructing GSSAP operators to focus on observing specific objects, use various maneuvers to increase stealth, and prevent the owners of those assets from detecting their approach.

Shaw says that the operators pushed back, saying that the satellites didn’t have enough fuel to make those moves and still be useful until the end of their useful lives.

That answer worried him. Understanding threats in space depends on being aware of the space domain, but these satellites’ limitations made it hard for them to do their job easily.

“I asked myself, ‘How much is this limiting us?'” “How did we get to this point where we’ve learned to be helpless and give up on going after certain targets?” Shaw asked. Shaw retired from Space Command in October 2023 and was named to Sierra Space’s strategic council group in February. “It was pretty important when we started to peel it back.”

As he shared his findings with others in Space Command, Shaw noted that the concerns began to escalate, evolving into a concept he refers to as dynamic space operations. The updated operational approach includes satellites that are more agile and can move more easily to examine the space environment or evade hostile threats or debris.

The concept of dynamic space operations relies on the presence of maintenance, mobility, and logistics technologies, such as refueling. Last year, Space Command urged the Space Force to promptly establish these capabilities.

The military responded quickly. The new procurement office, under the leadership of Col. Joyce Bulson, has been organizing tabletop exercises and preparing demonstrations to enhance the Space Force’s ability to satisfy operators’ current and future needs.

Bulson recently informed reporters that the Space Force is exploring the use of commercial technologies and capabilities being developed by NASA and DARPA in the mobility and logistics sectors.

DARPA is collaborating with SpaceLogistics, a division of Northrop Grumman, to develop a spacecraft for satellite repairs and upgrades under its Robotic Servicing of Geosynchronous Satellites program.

NASA, in collaboration with Maxar Technologies, was creating an on-orbit servicing and manufacturing vehicle specifically for satellite repairs. The agency terminated the $2 billion program on March 1 because of exceeding costs and delays.

Bulson stated during a media briefing on January 31 at the Space Mobility Conference in Orlando, Florida, that the technologies and concepts being discussed are built upon existing initiatives by others. “We are not attempting to replicate the current efforts.”

Rigorous analysis
The Space Force is considering conducting refueling demonstrations in the coming years to influence its future strategies. Astroscale U.S. was awarded a $25.5 million contract in September last year by the service to create a refueling spacecraft. The objective is to refuel a satellite using a vehicle in a test scheduled for 2026.

The service is collaborating with the Defense Innovation Unit, the Pentagon’s commercial technology hub, as part of its initiative. Orbit Fab, a Colorado-based company, will construct a fuel depot for Impulse Space’s orbiting servicing spacecraft, Mira. The depot will refill Astroscale’s vehicle using Orbit Fab’s Rapidly Attachable Fluid Transfer Interface, which transfers gas into the spacecraft. The system will also assist in a demonstration by the Air Force Research Laboratory known as Tetra-5.

In addition to refueling, the Space Force is exploring alternative technologies for providing satellites with extra propulsion, such as jetpacks that can be attached to spacecraft running low on fuel.

The acquisition team is planning refueling demonstrations, and the service is conducting further studies to enhance its understanding of how this capability will impact its involvement in future battles. A new Space Futures Command, focused on enhancing the service’s analytical precision, is expected to prioritize satellite refueling as one of its initial emerging mission objectives.

Doug Loverro, a former deputy assistant secretary of defense for space strategy and current independent consultant, emphasized the importance of the Space Force analyzing potential scenarios for refueling before implementing a formal program.

“There is much discussion, but there is a lack of analysis demonstrating the feasibility,” he stated. “A comprehensive analysis has not been conducted to determine the specific operational stage where this would be effective, the necessary requirements, and related details.”

Kennedy observed that Space Command has emphasized the necessity of a refueling capacity for its space domain awareness systems, suggesting that the service should also explore how other satellites and missions could leverage mobility and logistical capabilities. That includes transfer vehicles, which are specifically created to transport spacecraft to various orbits.

“If your only request is for GSSAP to have an extended duration,” he stated, “that does not align with the concept of dynamic space operations.”

Access and the resulting repercussions are crucial factors in achieving success by reaching all necessary destinations. “You need access to all the regimes,” he supplemented.

Signaling demand
The Space Force is developing procurement plans and constructing an analytical framework for refueling operations, but has not yet included financial requests for these efforts in its yearly budget submission. The organization has not used its own funds but has instead depended on additional allocations from Congress to cover expenses related to servicing, mobility, logistics demonstrations, and prototype projects. This included $30 million in fiscal 2023 to support its contract with Astroscale.

Bulson stated that the Space Force does not intend to allocate significant funds towards developing a specialized government satellite refueling capability. The service wants to emulate the practices of commercial enterprises in this field rather than becoming the anchor tenant.

Bulson informed reporters that they aim to maximize the use of commercial services. “We do not seek a substantial government investment to implement these capabilities.”

She declined to specify if the military will seek financing for space servicing endeavors in its FY25 budget, anticipated to be disclosed this month.

Several firms researching refueling capabilities and other service systems believe that the Space Force is the most suitable customer in the short term due to the lack of a compelling commercial business case for satellite refueling.

Erik Daehler, vice president of orbital systems and services for Sierra Space, stated that commercial satellites are more likely to be decommissioned due to the necessity of refilling their payloads rather than running out of fuel.

Companies are now focusing on deploying smaller, more cost-effective spacecraft with shorter mission durations into low Earth orbit, which is approximately 1,200 miles above the Earth’s surface. This trend has decreased the demand for refueling services.

“This suggests that the U.S. government is likely a main anchor tenant,” Daehler informed C4ISRNET.

Some firms believe that the military should have a more significant role in assisting the emerging market, even if a commercial business case develops. This involves conveying a more forceful demand message through regular funding and specific requirements.

Lauren Smith, in charge of Northrop’s in-space refueling initiatives, expressed that the Space Force’s creation of a program office focused on servicing, mobility, and logistics is a good move but insufficient.

Smith emphasized the need to have the technology listed as a line item in a budget for its advancement, as stated in C4ISRNET. The issue becomes how quickly they need our help if there isn’t enough money to address the urgency they’ve expressed. This will help to expedite and advance progress.

She mentioned that in addition to conveying its needs through financing and budget allocations, the Space Force would benefit from precise specifications from the Space Technologies Command to assist companies in designing technologies that align with the service’s military-specific objectives.

Smith emphasized the importance of minimizing redesign. “Having a clear understanding of their objectives from the beginning allows us to be more focused and effective.”

Interface protocols
Companies are urging the Space Force to set standards for the refueling ports or interfaces required by upcoming spacecraft.

The military collaborated with multiple firms to endorse interfaces that might be used as standards for the satellites. In January, it officially approved Northrop’s Passive Refueling Module as a viable option.

The Space Force is assessing interfaces from various companies, such as Orbit Fab, to expand the availability of designs for wider use.

Sierra Space’s Daehler emphasized the significance of creating common standards for companies building refueling and servicing capabilities to guarantee compatibility of interfaces.

He emphasized the urgent need for Sierra Space, the company developing the Dream Chaser spaceplane for NASA and targeting a 2025 launch of a fast demonstration platform.

“We seek a standard that can be universally accepted, ensuring its usability when we implement it,” Daehler stated. We must be prepared for launch in 2025 to meet our refueling requirements. A standard must be available immediately.