Such a milestone would put the fund in rare company: The fastest ETF to reach $1 billion was

State Street’s

SPDR Gold Trust

GLD -0.01%

fund, which hit the mark in just three days back in 2004.

“That speaks to the overall power of ARK right now,” said Nate Geraci, president of ETF Store, an investment-advisory firm. “At this point, investors think anything Cathie Wood touches turns to gold.”

The fund is ARK Investment Management LLC’s first launch in two years and stands in contrast to the lukewarm receptions its earlier products received. ARK’s flagship innovation fund, begun in 2014, took more than 3 1/2 years to reach $1 billion. Its last launch, the fintech innovation ETF in 2019, took about 21 months.

A lot has changed for ARK, though. In the span of a year, Ms. Wood’s ARK has transformed from a small, upstart manager of a handful of ETFs to one of the biggest fund managers in the U.S. The share prices of the firm’s five other actively managed ETFs doubled or tripled last year on the back of surging growth stocks such as

Tesla Inc.

and Roku Inc., earning Ms. Wood a cultlike following of individual investors who hang on her every tweet and video.

But those growth stocks are now the epicenter of a selloff that has left ARK’s older funds down at least 14% from their highs earlier this year. Rather than rolling out another fund primary tied to the tech trade, ARK has tilted nearly half of its space ETF toward manufacturers including

Lockheed Martin Corp.

,

Boeing Co.

and

Deere

DE 0.03%

& Co., a sector of the stock market that has benefited in recent months from rising interest rates and inflation expectations.

The fund is different enough for investors who say they are fans of Ms. Wood but also wary of plowing more money into a faltering tech trade.

“Most of Cathie’s ETFs are tech-heavy,” said Tré Diemer, 20 years old, a student at William & Mary who said he bought a couple of thousand dollars of ARKX shares Monday. “You look at this ETF and see a lot of names she hasn’t been as involved with.”

He already owns a variety of growth stocks and has been eyeing Ms. Wood’s other funds as a home for some of the money he earns from working as an emergency medical technician and running deliveries for

DoorDash Inc.

But tech and Ms. Wood’s other funds seemed overvalued, a point reinforced by the recent losses he said he sustained.

“You can look at this almost as a reopening ETF,” said Mr. Diemer, referring to underlying stocks poised to benefit most from a rebounding economy.

Not everyone is a fan of the fund’s makeup. Some took to social media, creating memes to mock ARK’s decision to include Deere and other companies that appear to have no significant ties to the fund’s theme of investing in space exploration and innovation. One showed a Deere tractor roving across a Mars landscape, another on the moon.

Deere, for its part, responded with several of its own memes, including one showing a UFO beaming up a tractor. Some analysts said the inclusion of Deere is less of a stretch when considering that the company makes satellite-guided machinery.

Other stocks included in the fund that seem at odds with its mandate include ARK’s passively managed 3D-printing ETF and shares of

Netflix Inc.

and

Amazon.com Inc.

Meanwhile, some of the few pure-play space stocks such as the satellite and imaging company

Maxar Technologies Inc.

didn’t make the cut. Neither did Rocket Lab USA Inc. nor Astra Space Inc., two rocket makers that are merging with blank-check companies to go public.

Ren Leggi,

a client portfolio manager at ARK, acknowledged that the holdings are causing some confusion but said that they are all in line with the fund’s mandate. “When we’re talking about space exploration and innovation, we define it as everything above ground,” said Mr. Leggi.

The advancement of drone technology plays a big part in why several companies, including Amazon, are in the fund, said Mr. Leggi. Netflix would benefit from the rollout of satellites that enable further adoption of broadband internet for streaming, and some rocket parts are 3D-printed, he added. As for the space companies left out, Mr. Leggi said valuations of some were too rich, especially those involved with special-purpose acquisition companies, while others didn’t pass their initial evaluation of whether the stock could sustain a 15% annualized return rate.

“We still continue to track a lot of companies in case we get a market environment where there’s a broader selloff and we can get in at an attractive price,” Mr. Leggi said.

Some investors remain unconvinced.

“I was not too fond of its holdings,” said Carter Wang, who is 19 and has roughly $3,000 in four of ARK’s earlier funds. He is a fan of Ms. Wood, citing her aggressive calls on Tesla as a key reason behind his decision to invest in several of the firm’s funds. But Mr. Wang, a business management economics major at the University of California, Santa Cruz, called the inclusion of ARK’s 3D-printing ETF odd, leading him to pass on the fund.

For several ARK investors, Ms. Wood’s past performance is key. With shares of ARKX trading around $21, some investors said they see a chance to get into the firm’s next success, likening it to ARK’s innovation fund, whose share price is six times higher since it launched in 2014 and continues to command investors’ attention. (The ETF saw record daily inflows one day last week, pulling in more than $700 million.)

“It doesn’t really bother me,” said James Carter, a 31-year-old tech writer in Washington, D.C., who snapped up shares on the space fund’s first day of trading. He said his mind was set on investing in the fund since he first heard about it earlier this year, even before any of its underlying stocks had been announced. He is holding out for the possibility that the fund ends up including shares of Elon Musk’s privately held rocket company, Space Exploration Technologies Corp.

“I was kind of late” with the other funds, Mr. Carter said of his other ARK investments. “So I specifically set money aside for the new ARK fund just because of my interest in ARK. I wanted to get in early.”

Write to Michael Wursthorn at Michael.Wursthorn@wsj.com