And if they had a medical issue or injury, home wouldn't be far away.
But for astronauts on future deep-space missions, like one to Mars, even a simple radio message might take up to 20 minutes to reach Earth. So how can they pack light and still bring all of the necessities, especially with an increased risk of injury during a six-month flight?
The answer could be what Dr. Julielynn Wong calls the "doctor's bag of the future": 3-D printing.
In January, Wong was the first to 3-D print a medical supply in space. Using a laser hand scan saved from the fitting process for space gloves, free software and a 3-D printer on the space station, she created a customized finger splint.
Hand injuries are common in astronauts. When they're in zero gravity, their hands and arms operate like their legs and feet since they grip and pull themselves from place to place rather than walking. Mallet finger injuries, which involve the tendon that straightens the end joint of fingers and thumbs, are the most common.
Finger splints may need to be worn for up to two months, coming off only once a day to clean the skin. Little holes in the splint allow the skin to breathe.
In addition to customizing the splints for the shape of astronauts' fingers, Wong arranged the holes into a star pattern.
Wong knew that the splints would work because in 2014, she and her colleagues printed 10 surgical instruments and tested them in a study against standard steel instruments. They worked equally well, but the 3-D ones could be printed in space -- or in rural and remote areas on Earth that lack access.
Wong combined her interests in public health and aerospace medicine -- for which she is dual board-certified -- to found 3D4MD, a company that 3-D prints medical supplies on-site wherever they are needed. Her "Medical Makers" around the world design medical tools and assistive devices, which can be created with free software and 3-D printers in libraries, clinics or someone's home.
The global community of innovators, patients and health care providers at 3D4MD has designed complex prosthetics for patients with missing or amputated limbs and simple solutions inspired by the needs of its own employees who have disabilities.
"We have hundreds of people across 10 countries crowdsourcing low-cost solutions to save lives, time and money," Wong said. "We have projects with humanitarian medical organizations like Doctors Without Borders to train workers on how to scan and 3-D print in the field."
This way, if medical equipment breaks in the field, Makers can design a digital fix for a part, ensure that it's printable and send it back in an email so the part may be printed on-site.
To help build the catalog of cheap, printable supplies, tools and devices, 3D4MD also hosts "make-a-thons" around the world. People of all ages, some who have never 3-D printed anythingcome together to brainstorm, design and create solutions to challenges that are presented.
Some of the items 3D4MD has designed and printed include simple solutions like a cupholder and bookstand that can be attached to a wheelchair as well as an insulin syringe handle that can be used by diabetes patients with limited use of their hands. The designs cost only a few dollars to make.
"We don't start designing solutions until we've met a patient or health care provider, because we have to understand their needs or challenges," Wong said. "We always ask them to take us through their day. And we want to empower patients to create the solutions they need the most."
Students design for space
The launch of the first 3-D printer to the space station in 2014 has inspired others with its potential, including a partnership between NASA and the American Society for Mechanical Engineers.
Together, they created Future Engineers, which issues two challenges a year to students from kindergarten to 12th grade to create 3-D designs for space.
Every challenge represents a real need that astronauts have identified, from tools and containers to food solutions and medical challenges that Mars astronauts may face. Experts judge the designs and interview with the finalists before declaring two winners, one under 13 and one over 13.
"These students are not only coming up with extremely innovative designs, but they're learning 3-D design skills that are imperative for the future of space and on Earth," said Deanne Bell, founder of Future Engineers.
The most recent challenge was to design a medical 3-D print that could be used for the journey to Mars. The two winning prints were a dual IV/syringe pump that overcomes the issue of zero gravity when administering IVs in space and a delivery device that astronauts can use to administer epinephrine and other drugs in self-treatment.
With 3-D printers showing up in classrooms across the country, students who may normally be turned off by math and science are realizing that they too can be engineers.
"It's extremely important to include the student aspect, because 3-D printing is a rapidly developing area, and we need skill sets to design functional parts that work," said Niki Werkheiser, NASA's In-space Manufacturing project manager. "Whether or not these kids go on to become engineers, and I think many of them will, seeing them feel that empowerment and controlling their destiny is extremely powerful, and those are the qualities we look for. So many of the problems we work through at NASA don't fit into a box."
Bell and Werkheiser, who work closely on Future Engineers, both wish they had had such opportunities when they were students.
"I was probably 18 before I held the first part in my hand that I designed on a computer," said Bell, a mechanical engineer. "These kids are making their ideas, printing and holding them and understanding the basics of engineering at a young age."
Werkheiser's department at NASA also works with universities and small businesses that are working on printable medical solutions for the future. Printable designs will be able to help astronauts with dental care, custom casts for fractures and sprains, sustainable tips for thermometers, vitamins, antibiotics, skin grafts and even food.
In turn, these devices can be used on Earth in remote areas that can't afford access to these items or types of care.
"So much of what we do at NASA is about making life better on Earth," Wekheiser said. "3-D printing evens the playing field so that you can create or make wherever you are.