I'm a big advocate for a 'core-and-satellite' investment strategy using ASX exchange-traded funds (ETFs) and index funds.

A core-and-satellite strategy involves using a handful of simple, broad-based, and low-cost index funds as the foundation of an investing portfolio.

This 'core' could consist of a combination of the BetaShares Australia 200 ETF (ASX: A200), the Vanguard MSCI Index International Shares ETF (ASX: VGS), the iShares S&P 500 ETF (ASX: IVV), or the Vanguard All-World ex-US Share Index ETF (ASX: VEU), for example. You could even throw in the iShares MSCI Emerging Markets ETF (ASX: IEM) for a bit of spice.

Whilst these core ETFs would form the lion's share of one's portfolio if one were to employ a core-and-satellite strategy, one can also branch out for some more speculative investments, or 'satellites', for a potential boost.

These investments might be riskier, but also possibly offer higher returns by outperforming the broader market.

These satellites could be individual stocks, perhaps something like Nvidia, Xero Ltd (ASX: XRO), or Pro Medicus Ltd (ASX: PME). They could also be other, sector or trend-specific ETFs of the non-index variety.

Two ASX ETFs that would make perfect satellites

Two that I would recommend as potential choices worthy of consideration would be the BetaShares Global Cybersecurity ETF (ASX: HACK) and the VanEck Global Defence ETF (ASX: DFND).

Both HACK and DFND are sector-specific funds that invest in a portfolio of global shares. These are all leaders in the cybersecurity and defence spaces, respectively.

Both of these industries have enormously powerful tailwinds behind them. This month's cyberattack on Qantas Airways Ltd (ASX: QAN) showcases the ever-growing dangers of our increasingly connected world. I think companies and governments will increasingly be willing to spend whatever it takes to avoid the reputational damage that a cyberattack can inflict.

HACK units have been comfortable market-beaters for years now, and I don't see why this won't continue.

It's a similar story with the VanEck Global Defence ETF. In this uncertain part of the 21st century, geopolitical tensions are unfortunately at their highest levels in decades. As a consequence, governments across the world are actively ramping up defence spending. This should benefit almost every company in DFND's portfolio.

Although this ETF only launched in September of last year, it has already risen more than 70%. Whilst I wouldn't expect those returns to continue at that magnitude, I think this fund still has market-beating potential going forward and thus is a worthy satellite in any portfolio.