The astronauts could float away in space while they spacewalk from the craft to the ISS, but to prevent that from happening, all astronauts use tethers to make sure that they do not get away from the spacecraft.
In 1973, Pete Conrad and Joe Kerwin were trying to repair a solar array on an extra-vehicular activity (EVA) on Skylab which suddenly deployed, and they were thrown off the space station. Their tethers kept them from floating away into space.
What could happen if the tether fails? NASA designed the Manned Maneuvering Unit (MMU) – a jet-powered backpack that allows the astronaut to control their movement in space. The MMU, packed with 11.4 kg of Nitrogen, was tested in 1984 in the first spacewalk without a tether.
The massive MMUs are no longer used and are replaced by Simplified Aid For EVA Rescue (SAFER). The SAFER is a device weighing only 1.4 kg that is attached to the backpack of the suit. The self-contained propulsive jetpack system is used in an emergency situation where an astronaut loses physical contact with the spacecraft. The SAFER will provide free-flying mobility to the crew member with a speed of 6-8 miles an hour, equivalent to that of a fast jog. Nonetheless, the speed is enough to carry the astronaut back to the space vessel.
The jetpack has been tested in controlled conditions in space. The most useful feature of it is that it helps to maintain the balance and keeps the astronaut from tumbling which is an arduous task, in itself.