In a recent article, I argued that the US needs the right of pre-emptive self-defense in space, which is exercised before an actual space attack has taken place. With an increasing budget, now is the time to invest in developing such a capability that could help deter a space war.

In his March 25 congressional testimony on the fiscal 2016 budget request for national security space activities, Douglas Loverro, deputy assistant secretary of defense for space policy, said the administration-initiated, interagency Strategic Portfolio Review "highlighted that whereas previously DoD and the Intelligence Community have focused primarily on providing capability from space — a difficult task on its own — now we must focus on the equally demanding and more complex task of assuring and defending our space capabilities against aggressive and comprehensive counterspace programs of others.

"On the DoD side, we either redirected or increased our planned budget on space security-related activities by about $5 billion over the next five fiscal years," and "we will carefully gauge if more is needed."

Space protection, defined here to include both space capability defense and space mission assurance, is "demanding" and "complex" especially when the protection must deal with growing traditional threats and potentially devastating new threats.

In my article, "Avoiding Space War Needs a New Approach," I considered close proximity operations in space, such as those under development in China, to be a game-changer. In peacetime, China could place in orbit space objects capable of close-proximity operations. During a crisis, such as seizing Taiwan, these space objects could be maneuvered to tailgate US satellites.

China could deter US intervention by demonstrating that its space stalkers could almost simultaneously attack several critical satellites from such a close proximity that the US would not have time to save them — if it waited until the attacks had actually started.

Pre-emptive self-defense could even be favored by proponents of an anti-satellite (ASAT) ban because pre-emption could serve as insurance to guard against space objects that appeared as satellites but actually were ASATs.

To be effective, pre-emptive self-defense must be enabled with defensive measures to protect satellites against this tailgating threat. In his testimony, Loverro described better anti-jam and anti-spoof technologies, more resilient next-generation satellites, life-extension of on-orbit legacy satellites, and partnerships with allied nations and commercial partners.

These space protection measures are aimed at the rapidly growing traditional space threats. Using these measures to counter this new tailgating threat would face two problems.

First, passive defenses, such as anti-jamming and evasive maneuver, would be either irrelevant or ineffective against space stalkers even if the defenses were executed pre-emptively, because space stalkers could dedicate much of their on-board resources, such as fuel and propulsion, for the sole purpose of attack, including chasing down an escaping target satellite.

Second, backups drawn from partners might have lower capability and take time to resume lost services, and partners might not be able to spare the full capacity requested by the US.

Thus, the US should undertake the following studies and investments to ensure a pre-emptive self-defense capability:

The Space Security and Defense Program (SSDP) established by the Defense Department and the National Intelligence Office should study how to best gain support from allies and others to promote pre-emptive self-defense.

In addition, the purpose of pre-emption is to prohibit the positioning of more than an innocuous threshold number of space objects to tailgate (or closely lead) another country's satellites. The SSDP should decide whether the threshold is two, three, four or other number. As there is no peaceful reason to tailgate so many satellites at the same time, the pre-emption can be restricted from being used as a pretext for aggression.

Space situational awareness programs should include real-time monitoring of space objects in, or quickly maneuverable into, close-proximity of US important satellites.

Some US ballistic missiles should be repurposed for disabling space stalkers, but designed in such a way to minimize debris. For example, the kill mechanism could spray paint a space stalker's sensors, or bend or cut its antennae and solar panels.

The US should develop capabilities such as jamming or spoofing the communications links used to control space stalkers. These temporary and reversible measures of disabling as opposed to physical destruction, could sway support from undecided nations.

Preemptive self-defense, once enabled, would protect satellites against this new tailgating threat and help deter a space Pearl Harbor.