Delayed voice communication
Introduction
Human exploration of deep space will involve significant delays for radio transmissions between crews in space and flight controllers on Earth. At the speed of light (3.00×108 m s−1, or almost exactly 1 Astronomical Unit per 500 s), the one-way delay is about 1.3 s for the Moon or an Earth-Moon libration point, 5 s for an Earth-Sun libration point, tens of seconds to a few minutes for accessible near-Earth asteroids (e.g., [1]), and up to 22 min for Mars at its 2.7 AU maximum distance from Earth. Command and telemetry delays of minutes to hours are routinely tolerated in the operation of unpiloted spacecraft (e.g., [2]). This paper explores the much less mature field of delayed voice communication between people.
Delayed communication is not new to human experience. Before the telephone and telegraph people corresponded with written letters. But delay is foreign to the operational concept of current human space missions, which rely on close and often time-critical cooperation between crews and controllers. The Apollo 13 mission might have had a less positive outcome if air-to-ground communication had traveled by post.
Delayed communication poses different problems than communication that is intermittent, but instantaneous when present, as in the earlier days of space exploration when spacecraft in low Earth orbit could talk with ground stations for a few minutes at a time. Both intermittent and delayed communication reduce the amount of information that can be exchanged by voice, but intermittent communication still allows normal human interaction when the link is present. Delayed communication makes normal conversation impossible, forcing operators to find different ways to communicate.
Delayed voice communication is part of the larger topic of crew autonomy, which has been addressed in other studies (e.g., [3], [4], [5], [6], [7]). Long delays mean that the ground segment is less able to help the crew, especially in cases that require fast action. The crew must therefore take responsibility in more situations. Flight rules must take into account the magnitude of the communication delay, the likely reaction time of flight and ground operators, and the time-to-effect of each possible action and malfunction, and must assign responsibility to the flight segment, the ground segment, or both in a way that adapts to the delay as it changes with the distance to Earth.
NASA has explored delayed voice communication in high-fidelity simulations of future space exploration missions. These space flight “analog” tests (e.g., [8]) are often conducted at remote field sites. They typically include fully staffed control centers, astronauts serving as crew, realistic mission timelines lasting one to two weeks, and prototype exploration vehicles and habitats. Analogs have yielded valuable insights into future space exploration architectures and operational concepts, and have field-tested dozens of emerging technologies, including countermeasures for delayed communication.
NASA Extreme Environment Mission Operations (NEEMO) [6], [9], [10] expeditions are approximately 10 days in duration. Six-person NEEMO crews live in the Aquarius undersea habitat, located off Key Largo, Florida at a depth of 20 m. Aquarius is an isolated, confined space with an outside environment that does not support human life. It is also a saturation-dive facility, so a quick return to the surface is not possible. NEEMO crews don diving gear to conduct “EVAs” outside the habitat, taking advantage of the water's buoyancy to simulate reduced or zero gravity. A mobile control center topside in Key Largo assists and monitors the “aquanauts.” The NEEMO 13 and NEEMO 14 missions employed 20-min one-way communication delays. NEEMO 16 modeled operations at a near-Earth asteroid with a 50-s one-way delay, and also employed 5- and 10-min one-way delays for two simulated emergency scenarios. The 50-s delay corresponds to a distance of 0.1 AU from Earth, a rough representative value for asteroids accessible for human exploration (e.g., [1]). For ease of comparison, the 50-s delay was also used in other analog tests.
Desert Research and Technology Studies (Desert RATS) [11] is a space mission simulation at a geologically interesting field site near Flagstaff, Arizona. Two- and four-person Desert RATS crews drive prototype rovers on one- to two-week missions that simulate traverses on the Moon or Mars, or that mimic operations on and near an asteroid. Wearing instrumented backpacks, they perform “EVAs” to evaluate tools and techniques for geological exploration. Crews camp in the rovers as well, providing insight for designers of vehicle cockpits and habitation spaces. As in NEEMO, a distant control center assists in the operation. Desert RATS 2011 simulated geological exploration of a near-Earth asteroid with a 50-s one-way delay.
Research and Technology Studies (RATS) [12] is a successor to Desert RATS, similar in duration and character but conducted indoors at NASA Johnson Space Center. Two- and four-person RATS crews live in prototype vehicles, but “fly” them in a computer-rendered simulation environment. Their “EVAs” are carried out in virtual-reality simulators and in winch-and-pulley facilities that offload the occupant's weight. RATS 2012 simulated operations at a near-Earth asteroid with a 50-s one-way delay. RATS 2012 also spent a few hours operating with one-way delays of 10 and 20 min.
The Pavilion Lake Research Project (PLRP) [13] is a scientific investigation that also serves as a space flight analog. It studies unusual stony microbial growths in remote mountain lakes in Canada by employing small one-person submersibles that are excellent stand-ins for spacecraft. As in NEEMO, the underwater environment poses real challenges and risks. The submersible “pilots” make science dives typically lasting 3–6 h, in close communication with scientists in the boats that track the subs. PLRP has investigated underwater science operations with a 50-s one-way delay.
Finally, the Autonomous Mission Operations (AMO) project [7] aimed to develop operational techniques to improve crew autonomy for the future exploration of deep space. Its series of 2-h mission simulations employed four-person crews, a full mission control center and flight control team, and a prototype spacecraft cabin with medium-fidelity systems models and remote command and telemetry capability. AMO formally tested 50- and 300-s one-way delays of voice, commands, and telemetry.
This paper presents the lessons learned about delayed voice communication from those tests, gleaned from feedback given by crews, Capcoms, controllers, and other participants. It is intended to inform future ground tests and, eventually, actual human deep-space exploration missions.
Section snippets
Challenges of delayed voice communication
The crews of RATS and NEEMO developed consensus reports [14] for many of the conditions and technologies they tested using a formal 10-point “acceptability” scale developed specifically for analog missions and used since 2008 (e.g., [12]). The scale is defined as follows:
1–2 totally acceptable, no improvements necessary;
3–4 acceptable, minor improvements desired;
5–6 borderline, improvements warranted;
7–8 unacceptable, improvements required;
9–10 totally unacceptable, major improvements required.
Operator recommendations
The space flight analog tests that exposed the challenges of delayed voice communication listed in Section 2 also yielded suggestions for how to meet those challenges. These recommendations were gathered from debrief comments and other unstructured feedback from the participants. The suggestions were remarkably similar and consistent despite the differences among the tests; there were no significant outlying opinions or dissenting voices. All of the recorded responses are given below and keyed
Comparing different delay magnitudes
The AMO test [7] formally compared the same mission scenario with different values of the communication delay. It yielded an interesting insight about the challenge of voice communication at different delays. In comparing participant responses from tests at 50 and 300 s delay, there was no general agreement as to which was more difficult. Although all of the challenges in Section 2 become greater with longer delays, some interviewees felt that 50 s was worse, possibly because they were trying to
Conclusion
In this paper, we report results from 3 years of operational tests investigating the delayed voice communication that will be a hallmark of the future human exploration of deep space. The tests identified many challenges: confusion of sequence, blocked calls, wasted crew time, reduced ability to provide relevant information, losing track of which parties have heard which messages, threatened rapport between crew and ground, slow response to emerging events, and generally reduced situational
Acknowledgments
NASA funding supported this work. The authors thank David Korth, Steve Rader, Vanessa Wyche, and Bernadette Hajek for their helpful feedback. The authors are also grateful to an anonymous reviewer whose insightful comments improved this paper.
Stanley G. Love is a NASA astronaut at Johnson Space Center in Houston. He served as a crew member and spacewalker on Shuttle flight STS-122 in 2008, worked as a Capcom for many Shuttle and Station missions, and participated in several terrestrial spaceflight analog expeditions. He previously worked as a spacecraft engineer at JPL and as a postdoctoral researcher in planetary science at Caltech and at the University of Hawaii, studying asteroids, meteorites, cosmic dust, and hypervelocity
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Stanley G. Love is a NASA astronaut at Johnson Space Center in Houston. He served as a crew member and spacewalker on Shuttle flight STS-122 in 2008, worked as a Capcom for many Shuttle and Station missions, and participated in several terrestrial spaceflight analog expeditions. He previously worked as a spacecraft engineer at JPL and as a postdoctoral researcher in planetary science at Caltech and at the University of Hawaii, studying asteroids, meteorites, cosmic dust, and hypervelocity impacts. He holds a BS in Physics from Harvey Mudd College, and an MS and Ph.D. in Astronomy from the University of Washington.
Marcum L. Reagan is the Deputy Project Manager for the Analogs Project at Johnson Space Center in Houston. He served as an aquanaut crew member on the second NASA Extreme Environment Mission Operations (NEEMO) mission in the Aquarius Undersea Habitat, and was a crewmember for the Research and Technology Studies (RATS) 2012 mission. He was the Mission Director for many of the NEEMO missions, including NEEMO 16, and has been an ISS Capcom for the past 10 years. He holds a BS in Aerospace Engineering from Texas A&M University, and an MS in Aerospace Engineering Sciences from the University of Colorado.